diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9740d82d21460..2e8f0ff2ae692 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5915,9 +5915,6 @@ namespace ts {
                 if (parameterDeclaration && isRequiredInitializedParameter(parameterDeclaration)) {
                     parameterType = getOptionalType(parameterType);
                 }
-                if ((context.flags & NodeBuilderFlags.NoUndefinedOptionalParameterType) && parameterDeclaration && !isJSDocParameterTag(parameterDeclaration) && isOptionalUninitializedParameter(parameterDeclaration)) {
-                    parameterType = getTypeWithFacts(parameterType, TypeFacts.NEUndefined);
-                }
                 const parameterTypeNode = serializeTypeForDeclaration(context, parameterType, parameterSymbol, context.enclosingDeclaration, privateSymbolVisitor, bundledImports);
 
                 const modifiers = !(context.flags & NodeBuilderFlags.OmitParameterModifiers) && preserveModifierFlags && parameterDeclaration && parameterDeclaration.modifiers ? parameterDeclaration.modifiers.map(factory.cloneNode) : undefined;
@@ -6544,7 +6541,7 @@ namespace ts {
                     if (declWithExistingAnnotation && !isFunctionLikeDeclaration(declWithExistingAnnotation) && !isGetAccessorDeclaration(declWithExistingAnnotation)) {
                         // try to reuse the existing annotation
                         const existing = getEffectiveTypeAnnotationNode(declWithExistingAnnotation)!;
-                        if (getTypeFromTypeNode(existing) === type && existingTypeNodeIsNotReferenceOrIsReferenceWithCompatibleTypeArgumentCount(existing, type)) {
+                        if (typeNodeIsEquivalentToType(existing, declWithExistingAnnotation, type) && existingTypeNodeIsNotReferenceOrIsReferenceWithCompatibleTypeArgumentCount(existing, type)) {
                             const result = serializeExistingTypeNode(context, existing, includePrivateSymbol, bundled);
                             if (result) {
                                 return result;
@@ -6562,6 +6559,17 @@ namespace ts {
                 return result;
             }
 
+            function typeNodeIsEquivalentToType(typeNode: TypeNode, annotatedDeclaration: Declaration, type: Type) {
+                const typeFromTypeNode = getTypeFromTypeNode(typeNode);
+                if (typeFromTypeNode === type) {
+                    return true;
+                }
+                if (isParameter(annotatedDeclaration) && annotatedDeclaration.questionToken) {
+                    return getTypeWithFacts(type, TypeFacts.NEUndefined) === typeFromTypeNode;
+                }
+                return false;
+            }
+
             function serializeReturnTypeForSignature(context: NodeBuilderContext, type: Type, signature: Signature, includePrivateSymbol?: (s: Symbol) => void, bundled?: boolean) {
                 if (!isErrorType(type) && context.enclosingDeclaration) {
                     const annotation = signature.declaration && getEffectiveReturnTypeNode(signature.declaration);
@@ -42579,12 +42587,6 @@ namespace ts {
                 hasSyntacticModifier(parameter, ModifierFlags.ParameterPropertyModifier);
         }
 
-        function isOptionalUninitializedParameter(parameter: ParameterDeclaration) {
-            return !!strictNullChecks &&
-                isOptionalParameter(parameter) &&
-                !parameter.initializer;
-        }
-
         function isExpandoFunctionDeclaration(node: Declaration): boolean {
             const declaration = getParseTreeNode(node, isFunctionDeclaration);
             if (!declaration) {
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 9ae7d10b07cea..0831da97a629c 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -4490,7 +4490,6 @@ namespace ts {
         UseAliasDefinedOutsideCurrentScope      = 1 << 14,  // Allow non-visible aliases
         UseSingleQuotesForStringLiteralType     = 1 << 28,  // Use single quotes for string literal type
         NoTypeReduction                         = 1 << 29,  // Don't call getReducedType
-        NoUndefinedOptionalParameterType        = 1 << 30,  // Do not add undefined to optional parameter type
 
         // Error handling
         AllowThisInObjectLiteral                = 1 << 15,
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 3b303c65eb83f..ca7155c30cacd 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -7659,4 +7659,8 @@ namespace ts {
 
         return state > States.NodeModules ? { topLevelNodeModulesIndex, topLevelPackageNameIndex, packageRootIndex, fileNameIndex } : undefined;
     }
+
+    export function getParameterTypeNode(parameter: ParameterDeclaration | JSDocParameterTag) {
+        return parameter.kind === SyntaxKind.JSDocParameterTag ? parameter.typeExpression?.type : parameter.type;
+    }
 }
diff --git a/src/services/codefixes/helpers.ts b/src/services/codefixes/helpers.ts
index a33fe54ec2a7f..28fccba8190e3 100644
--- a/src/services/codefixes/helpers.ts
+++ b/src/services/codefixes/helpers.ts
@@ -194,7 +194,6 @@ namespace ts.codefix {
         const scriptTarget = getEmitScriptTarget(program.getCompilerOptions());
         const flags =
             NodeBuilderFlags.NoTruncation
-            | NodeBuilderFlags.NoUndefinedOptionalParameterType
             | NodeBuilderFlags.SuppressAnyReturnType
             | NodeBuilderFlags.AllowEmptyTuple
             | (quotePreference === QuotePreference.Single ? NodeBuilderFlags.UseSingleQuotesForStringLiteralType : NodeBuilderFlags.None);
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 9ea997539f55f..6146af8bb9f75 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -2394,7 +2394,6 @@ declare namespace ts {
         UseAliasDefinedOutsideCurrentScope = 16384,
         UseSingleQuotesForStringLiteralType = 268435456,
         NoTypeReduction = 536870912,
-        NoUndefinedOptionalParameterType = 1073741824,
         AllowThisInObjectLiteral = 32768,
         AllowQualifiedNameInPlaceOfIdentifier = 65536,
         /** @deprecated AllowQualifedNameInPlaceOfIdentifier. Use AllowQualifiedNameInPlaceOfIdentifier instead. */
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 45eed1b64845b..22af7579a0367 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -2394,7 +2394,6 @@ declare namespace ts {
         UseAliasDefinedOutsideCurrentScope = 16384,
         UseSingleQuotesForStringLiteralType = 268435456,
         NoTypeReduction = 536870912,
-        NoUndefinedOptionalParameterType = 1073741824,
         AllowThisInObjectLiteral = 32768,
         AllowQualifiedNameInPlaceOfIdentifier = 65536,
         /** @deprecated AllowQualifedNameInPlaceOfIdentifier. Use AllowQualifiedNameInPlaceOfIdentifier instead. */
diff --git a/tests/baselines/reference/arrayFakeFlatNoCrashInferenceDeclarations.types b/tests/baselines/reference/arrayFakeFlatNoCrashInferenceDeclarations.types
index fd8dccc975c77..692e007dd92ba 100644
--- a/tests/baselines/reference/arrayFakeFlatNoCrashInferenceDeclarations.types
+++ b/tests/baselines/reference/arrayFakeFlatNoCrashInferenceDeclarations.types
@@ -19,7 +19,7 @@ type BadFlatArray<Arr, Depth extends number> = {obj: {
 >1 : 1
 
 declare function flat<A, D extends number = 1>(
->flat : <A, D extends number = 1>(arr: A, depth?: D | undefined) => BadFlatArray<A, D>[]
+>flat : <A, D extends number = 1>(arr: A, depth?: D) => BadFlatArray<A, D>[]
 
     arr: A,
 >arr : A
diff --git a/tests/baselines/reference/assertionTypePredicates1.types b/tests/baselines/reference/assertionTypePredicates1.types
index e72b3077c9b95..064cf6066f4dd 100644
--- a/tests/baselines/reference/assertionTypePredicates1.types
+++ b/tests/baselines/reference/assertionTypePredicates1.types
@@ -270,7 +270,7 @@ namespace Debug {
 >Debug : typeof Debug
 
     export declare function assert(value: unknown, message?: string): asserts value;
->assert : (value: unknown, message?: string | undefined) => asserts value
+>assert : (value: unknown, message?: string) => asserts value
 >value : unknown
 >message : string | undefined
 
diff --git a/tests/baselines/reference/asyncFunctionsAndStrictNullChecks.types b/tests/baselines/reference/asyncFunctionsAndStrictNullChecks.types
index 33ccf9c331fcc..f67fe49a61fb0 100644
--- a/tests/baselines/reference/asyncFunctionsAndStrictNullChecks.types
+++ b/tests/baselines/reference/asyncFunctionsAndStrictNullChecks.types
@@ -75,7 +75,7 @@ declare function resolve2<T>(value: T): Windows.Foundation.IPromise<T>;
 >Foundation : any
 
 async function sample2(x?: number) {
->sample2 : (x?: number | undefined) => Promise<void>
+>sample2 : (x?: number) => Promise<void>
 >x : number | undefined
 
     let x1 = await resolve1(x);
diff --git a/tests/baselines/reference/callsOnComplexSignatures.types b/tests/baselines/reference/callsOnComplexSignatures.types
index a255300662666..192c64474400f 100644
--- a/tests/baselines/reference/callsOnComplexSignatures.types
+++ b/tests/baselines/reference/callsOnComplexSignatures.types
@@ -110,7 +110,7 @@ function test3(items: string[] | number[]) {
 }
 
 function test4(
->test4 : (arg1: ((...objs: {    x: number;}[]) => number) | ((...objs: {    y: number;}[]) => number), arg2: ((a: {    x: number;}, b: object) => number) | ((a: object, b: {    x: number;}) => number), arg3: ((a: {    x: number;}, ...objs: {    y: number;}[]) => number) | ((...objs: {    x: number;}[]) => number), arg4: ((a?: { x: number; } | undefined, b?: { x: number; } | undefined) => number) | ((a?: { y: number; } | undefined) => number), arg5: ((a?: { x: number; } | undefined, ...b: {    x: number;}[]) => number) | ((a?: { y: number; } | undefined) => number), arg6: ((a?: { x: number; } | undefined, b?: { x: number; } | undefined) => number) | ((...a: {    y: number;}[]) => number)) => void
+>test4 : (arg1: ((...objs: {    x: number;}[]) => number) | ((...objs: {    y: number;}[]) => number), arg2: ((a: {    x: number;}, b: object) => number) | ((a: object, b: {    x: number;}) => number), arg3: ((a: {    x: number;}, ...objs: {    y: number;}[]) => number) | ((...objs: {    x: number;}[]) => number), arg4: ((a?: {    x: number;}, b?: {    x: number;}) => number) | ((a?: {    y: number;}) => number), arg5: ((a?: {    x: number;}, ...b: {    x: number;}[]) => number) | ((a?: {    y: number;}) => number), arg6: ((a?: {    x: number;}, b?: {    x: number;}) => number) | ((...a: {    y: number;}[]) => number)) => void
 
     arg1: ((...objs: {x: number}[]) => number) | ((...objs: {y: number}[]) => number),
 >arg1 : ((...objs: {    x: number;}[]) => number) | ((...objs: {    y: number;}[]) => number)
@@ -138,7 +138,7 @@ function test4(
 >x : number
 
     arg4: ((a?: {x: number}, b?: {x: number}) => number) | ((a?: {y: number}) => number),
->arg4 : ((a?: { x: number; } | undefined, b?: { x: number; } | undefined) => number) | ((a?: { y: number; } | undefined) => number)
+>arg4 : ((a?: {    x: number;}, b?: {    x: number;}) => number) | ((a?: {    y: number;}) => number)
 >a : { x: number; } | undefined
 >x : number
 >b : { x: number; } | undefined
@@ -147,7 +147,7 @@ function test4(
 >y : number
 
     arg5: ((a?: {x: number}, ...b: {x: number}[]) => number) | ((a?: {y: number}) => number),
->arg5 : ((a?: { x: number; } | undefined, ...b: {    x: number;}[]) => number) | ((a?: { y: number; } | undefined) => number)
+>arg5 : ((a?: {    x: number;}, ...b: {    x: number;}[]) => number) | ((a?: {    y: number;}) => number)
 >a : { x: number; } | undefined
 >x : number
 >b : { x: number; }[]
@@ -156,7 +156,7 @@ function test4(
 >y : number
 
     arg6: ((a?: {x: number}, b?: {x: number}) => number) | ((...a: {y: number}[]) => number),
->arg6 : ((a?: { x: number; } | undefined, b?: { x: number; } | undefined) => number) | ((...a: {    y: number;}[]) => number)
+>arg6 : ((a?: {    x: number;}, b?: {    x: number;}) => number) | ((...a: {    y: number;}[]) => number)
 >a : { x: number; } | undefined
 >x : number
 >b : { x: number; } | undefined
@@ -339,7 +339,7 @@ function test5() {
 
     // Pair of non-like intrinsics
     function render(url?: string): React.ReactNode {
->render : (url?: string | undefined) => React.ReactNode
+>render : (url?: string) => React.ReactNode
 >url : string | undefined
 >React : any
 
diff --git a/tests/baselines/reference/circularOptionalityRemoval.types b/tests/baselines/reference/circularOptionalityRemoval.types
index 5783b24a6c379..f35bd580699b7 100644
--- a/tests/baselines/reference/circularOptionalityRemoval.types
+++ b/tests/baselines/reference/circularOptionalityRemoval.types
@@ -12,7 +12,7 @@ function fn1(x: number | undefined = x > 0 ? x : 0) { }
 
 // Report from user
 function fn2(x?: string = someCondition ? 'value1' : x) { }
->fn2 : (x?: string | undefined) => void
+>fn2 : (x?: string) => void
 >x : string | undefined
 >someCondition ? 'value1' : x : string | undefined
 >someCondition : any
diff --git a/tests/baselines/reference/contextuallyTypedParametersWithInitializers.types b/tests/baselines/reference/contextuallyTypedParametersWithInitializers.types
index db65878b320d3..e39e3bde4d733 100644
--- a/tests/baselines/reference/contextuallyTypedParametersWithInitializers.types
+++ b/tests/baselines/reference/contextuallyTypedParametersWithInitializers.types
@@ -21,7 +21,7 @@ declare function id4<T extends (x: { foo?: number }) => any>(input: T): T;
 >input : T
 
 declare function id5<T extends (x?: number) => any>(input: T): T;
->id5 : <T extends (x?: number | undefined) => any>(input: T) => T
+>id5 : <T extends (x?: number) => any>(input: T) => T
 >x : number | undefined
 >input : T
 
diff --git a/tests/baselines/reference/controlFlowAliasing.types b/tests/baselines/reference/controlFlowAliasing.types
index b7c73a1d9fa62..1f97602b3f290 100644
--- a/tests/baselines/reference/controlFlowAliasing.types
+++ b/tests/baselines/reference/controlFlowAliasing.types
@@ -532,7 +532,7 @@ function f27(outer: { obj: { kind: 'foo', foo: string } | { kind: 'bar', bar: nu
 }
 
 function f28(obj?: { kind: 'foo', foo: string } | { kind: 'bar', bar: number }) {
->f28 : (obj?: { kind: 'foo'; foo: string; } | { kind: 'bar'; bar: number; } | undefined) => void
+>f28 : (obj?: {    kind: 'foo';    foo: string;} | {    kind: 'bar';    bar: number;}) => void
 >obj : { kind: 'foo'; foo: string; } | { kind: 'bar'; bar: number; } | undefined
 >kind : "foo"
 >foo : string
diff --git a/tests/baselines/reference/controlFlowForIndexSignatures.types b/tests/baselines/reference/controlFlowForIndexSignatures.types
index 94db82e959c44..20fff99f2c158 100644
--- a/tests/baselines/reference/controlFlowForIndexSignatures.types
+++ b/tests/baselines/reference/controlFlowForIndexSignatures.types
@@ -10,7 +10,7 @@ const boo: Foo = { bar: 'bar' };
 >'bar' : "bar"
 
 function a(aboo1?: Foo) {
->a : (aboo1?: Foo | undefined) => void
+>a : (aboo1?: Foo) => void
 >aboo1 : Foo | undefined
 
     if (!aboo1) return;
diff --git a/tests/baselines/reference/controlFlowOptionalChain.types b/tests/baselines/reference/controlFlowOptionalChain.types
index 823d07ca8bf7d..8eb843fb0600b 100644
--- a/tests/baselines/reference/controlFlowOptionalChain.types
+++ b/tests/baselines/reference/controlFlowOptionalChain.types
@@ -1882,7 +1882,7 @@ type Shape =
 >radius : number
 
 function getArea(shape?: Shape) {
->getArea : (shape?: Shape | undefined) => number
+>getArea : (shape?: Shape) => number
 >shape : Shape | undefined
 
     switch (shape?.type) {
diff --git a/tests/baselines/reference/defaultParameterAddsUndefinedWithStrictNullChecks.types b/tests/baselines/reference/defaultParameterAddsUndefinedWithStrictNullChecks.types
index 2d6e2966a2dd9..06b51c2eeace6 100644
--- a/tests/baselines/reference/defaultParameterAddsUndefinedWithStrictNullChecks.types
+++ b/tests/baselines/reference/defaultParameterAddsUndefinedWithStrictNullChecks.types
@@ -1,6 +1,6 @@
 === tests/cases/compiler/defaultParameterAddsUndefinedWithStrictNullChecks.ts ===
 function f(addUndefined1 = "J", addUndefined2?: number) {
->f : (addUndefined1?: string, addUndefined2?: number | undefined) => number
+>f : (addUndefined1?: string, addUndefined2?: number) => number
 >addUndefined1 : string
 >"J" : "J"
 >addUndefined2 : number | undefined
diff --git a/tests/baselines/reference/destructureOptionalParameter.types b/tests/baselines/reference/destructureOptionalParameter.types
index 984b2da856ae7..01b45c1cb4bf4 100644
--- a/tests/baselines/reference/destructureOptionalParameter.types
+++ b/tests/baselines/reference/destructureOptionalParameter.types
@@ -1,6 +1,6 @@
 === tests/cases/compiler/destructureOptionalParameter.ts ===
 declare function f1({ a, b }?: { a: number, b: string }): void;
->f1 : ({ a, b }?: { a: number; b: string; } | undefined) => void
+>f1 : ({ a, b }?: {    a: number;    b: string;}) => void
 >a : number
 >b : string
 >a : number
diff --git a/tests/baselines/reference/destructuringAssignmentWithDefault.types b/tests/baselines/reference/destructuringAssignmentWithDefault.types
index 379bfe8b3bdbd..170d1d26ba509 100644
--- a/tests/baselines/reference/destructuringAssignmentWithDefault.types
+++ b/tests/baselines/reference/destructuringAssignmentWithDefault.types
@@ -61,7 +61,7 @@ function f1(options?: { color?: string, width?: number }) {
 }
 
 function f2(options?: [string?, number?]) {
->f2 : (options?: [(string | undefined)?, (number | undefined)?] | undefined) => void
+>f2 : (options?: [string?, number?]) => void
 >options : [(string | undefined)?, (number | undefined)?] | undefined
 
     let [str, num] = options || [];
@@ -133,7 +133,7 @@ function f3(options?: { color: string, width: number }) {
 }
 
 function f4(options?: [string, number]) {
->f4 : (options?: [string, number] | undefined) => void
+>f4 : (options?: [string, number]) => void
 >options : [string, number] | undefined
 
     let [str, num] = options || [];
diff --git a/tests/baselines/reference/genericFunctionInference1.types b/tests/baselines/reference/genericFunctionInference1.types
index d76a85dd43d85..9dd28cea1a72e 100644
--- a/tests/baselines/reference/genericFunctionInference1.types
+++ b/tests/baselines/reference/genericFunctionInference1.types
@@ -801,7 +801,7 @@ const fn20 = pipe((_a?: {}) => 1);
 >fn20 : (_a?: {} | undefined) => number
 >pipe((_a?: {}) => 1) : (_a?: {} | undefined) => number
 >pipe : { <A extends any[], B>(ab: (...args: A) => B): (...args: A) => B; <A extends any[], B, C>(ab: (...args: A) => B, bc: (b: B) => C): (...args: A) => C; <A extends any[], B, C, D>(ab: (...args: A) => B, bc: (b: B) => C, cd: (c: C) => D): (...args: A) => D; }
->(_a?: {}) => 1 : (_a?: {} | undefined) => number
+>(_a?: {}) => 1 : (_a?: {}) => number
 >_a : {} | undefined
 >1 : 1
 
@@ -968,7 +968,7 @@ const fn62 = pipe(
 // Repro from #30297
 
 declare function foo2<T, U = T>(fn: T, a?: U, b?: U): [T, U];
->foo2 : <T, U = T>(fn: T, a?: U | undefined, b?: U | undefined) => [T, U]
+>foo2 : <T, U = T>(fn: T, a?: U, b?: U) => [T, U]
 >fn : T
 >a : U | undefined
 >b : U | undefined
diff --git a/tests/baselines/reference/genericRestParameters1.types b/tests/baselines/reference/genericRestParameters1.types
index 687ab9751ddec..cbc4e9410755c 100644
--- a/tests/baselines/reference/genericRestParameters1.types
+++ b/tests/baselines/reference/genericRestParameters1.types
@@ -570,7 +570,7 @@ f23();
 >f23 : () => string[]
 
 declare const g20: (x: number, y?: string, z?: boolean) => string[];
->g20 : (x: number, y?: string | undefined, z?: boolean | undefined) => string[]
+>g20 : (x: number, y?: string, z?: boolean) => string[]
 >x : number
 >y : string | undefined
 >z : boolean | undefined
diff --git a/tests/baselines/reference/indexedAccessNormalization.types b/tests/baselines/reference/indexedAccessNormalization.types
index 53d57f4319ae7..418be2989a710 100644
--- a/tests/baselines/reference/indexedAccessNormalization.types
+++ b/tests/baselines/reference/indexedAccessNormalization.types
@@ -11,7 +11,7 @@ type MyMap<M extends object> = {
 }
 
 declare function g<T>(value?: T): void;
->g : <T>(value?: T | undefined) => void
+>g : <T>(value?: T) => void
 >value : T | undefined
 
 function f1<M extends object>(mymap: MyMap<M>, k: keyof M) {
diff --git a/tests/baselines/reference/inferFromBindingPattern.types b/tests/baselines/reference/inferFromBindingPattern.types
index 802fd56f7fcc3..ee217fafa8617 100644
--- a/tests/baselines/reference/inferFromBindingPattern.types
+++ b/tests/baselines/reference/inferFromBindingPattern.types
@@ -60,7 +60,7 @@ interface Person {
 }
 
 declare function selectJohn<K = Person>(props?: SelectProps<Person, K>): SelectResult<Person, K>;
->selectJohn : <K = Person>(props?: SelectProps<Person, K> | undefined) => SelectResult<Person, K>
+>selectJohn : <K = Person>(props?: SelectProps<Person, K>) => SelectResult<Person, K>
 >props : SelectProps<Person, K> | undefined
 
 const [person] = selectJohn();
@@ -91,7 +91,7 @@ declare function makeTuple<T1>(arg: T1): [T1];
 >arg : T1
 
 declare function stringy<T = string>(arg?: T): T;
->stringy : <T = string>(arg?: T | undefined) => T
+>stringy : <T = string>(arg?: T) => T
 >arg : T | undefined
 
 const isStringTuple = makeTuple(stringy());  // [string]
diff --git a/tests/baselines/reference/inferenceErasedSignatures.types b/tests/baselines/reference/inferenceErasedSignatures.types
index 84f64ffda5682..382cc08394ff8 100644
--- a/tests/baselines/reference/inferenceErasedSignatures.types
+++ b/tests/baselines/reference/inferenceErasedSignatures.types
@@ -15,7 +15,7 @@ abstract class SomeAbstractClass<C, M, R> extends SomeBaseClass {
 >SomeBaseClass : SomeBaseClass
 
     foo!: (r?: R) => void;
->foo : (r?: R | undefined) => void
+>foo : (r?: R) => void
 >r : R | undefined
 
     bar!: (r?: any) => void;
@@ -72,7 +72,7 @@ interface BaseType<T1, T2>  {
 >c : T1
 
     useT2(r?: T2): void;
->useT2 : (r?: T2 | undefined) => void
+>useT2 : (r?: T2) => void
 >r : T2 | undefined
 
     unrelatedButSomehowRelevant(r?: any): void;
@@ -99,7 +99,7 @@ interface StructuralVersion  {
 >c : number
 
     useT2(r?: boolean): void;
->useT2 : (r?: boolean | undefined) => void
+>useT2 : (r?: boolean) => void
 >r : boolean | undefined
 
     unrelatedButSomehowRelevant(r?: any): void;
diff --git a/tests/baselines/reference/initializedParameterBeforeNonoptionalNotOptional.types b/tests/baselines/reference/initializedParameterBeforeNonoptionalNotOptional.types
index 5035da7bcef17..2656522f57e08 100644
--- a/tests/baselines/reference/initializedParameterBeforeNonoptionalNotOptional.types
+++ b/tests/baselines/reference/initializedParameterBeforeNonoptionalNotOptional.types
@@ -1,6 +1,6 @@
 === tests/cases/compiler/index.d.ts ===
 export declare function foo({a}?: {
->foo : ({ a }?: { a?: string | undefined; } | undefined) => void
+>foo : ({ a }?: {    a?: string;}) => void
 >a : string | undefined
 
     a?: string;
diff --git a/tests/baselines/reference/intersectionWithConflictingPrivates.types b/tests/baselines/reference/intersectionWithConflictingPrivates.types
index 62861bb4ec597..d7f8e4a9dedaa 100644
--- a/tests/baselines/reference/intersectionWithConflictingPrivates.types
+++ b/tests/baselines/reference/intersectionWithConflictingPrivates.types
@@ -138,7 +138,7 @@ class Foo {
 	}
 
   private async bar(node: CommitFileNode | ResultsFileNode | StashFileNode | StatusFileNode, options?: {}) {
->bar : (node: CommitFileNode | ResultsFileNode | StashFileNode | StatusFileNode, options?: {} | undefined) => Promise<undefined>
+>bar : (node: CommitFileNode | ResultsFileNode | StashFileNode | StatusFileNode, options?: {}) => Promise<undefined>
 >node : CommitFileNode | ResultsFileNode | StashFileNode | StatusFileNode
 >options : {} | undefined
 
diff --git a/tests/baselines/reference/jsDeclarationsReactComponents.js b/tests/baselines/reference/jsDeclarationsReactComponents.js
index 9c0373e83e739..fb0972b36ed3a 100644
--- a/tests/baselines/reference/jsDeclarationsReactComponents.js
+++ b/tests/baselines/reference/jsDeclarationsReactComponents.js
@@ -216,7 +216,7 @@ declare const TabbedShowLayout: {
     };
 } & ((props?: {
     elem: string;
-} | undefined) => JSX.Element);
+}) => JSX.Element);
 //// [jsDeclarationsReactComponents4.d.ts]
 export default TabbedShowLayout;
 declare function TabbedShowLayout(prop: {
diff --git a/tests/baselines/reference/jsxNamespaceGlobalReexport.types b/tests/baselines/reference/jsxNamespaceGlobalReexport.types
index 12226ae9e13a1..655a3a7cab9d9 100644
--- a/tests/baselines/reference/jsxNamespaceGlobalReexport.types
+++ b/tests/baselines/reference/jsxNamespaceGlobalReexport.types
@@ -90,7 +90,7 @@ import { JSXInternal } from '..';
 >JSXInternal : any
 
 export function jsx(
->jsx : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild;}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; }
+>jsx : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild;}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -110,7 +110,7 @@ export function jsx(
 
 ): VNode<any>;
 export function jsx<P>(
->jsx : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild;}, key?: string | undefined): VNode<any>; }
+>jsx : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild;}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
@@ -125,7 +125,7 @@ export function jsx<P>(
 ): VNode<any>;
 
 export function jsxs(
->jsxs : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild[];}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; }
+>jsxs : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild[];}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -145,7 +145,7 @@ export function jsxs(
 
 ): VNode<any>;
 export function jsxs<P>(
->jsxs : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild[];}, key?: string | undefined): VNode<any>; }
+>jsxs : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild[];}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
@@ -160,7 +160,7 @@ export function jsxs<P>(
 ): VNode<any>;
 
 export function jsxDEV(
->jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChildren;}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; }
+>jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChildren;}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -180,7 +180,7 @@ export function jsxDEV(
 
 ): VNode<any>;
 export function jsxDEV<P>(
->jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChildren;}, key?: string | undefined): VNode<any>; }
+>jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChildren;}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
diff --git a/tests/baselines/reference/jsxNamespaceGlobalReexportMissingAliasTarget.types b/tests/baselines/reference/jsxNamespaceGlobalReexportMissingAliasTarget.types
index 2e27ccbfa7433..99dcad4b53f95 100644
--- a/tests/baselines/reference/jsxNamespaceGlobalReexportMissingAliasTarget.types
+++ b/tests/baselines/reference/jsxNamespaceGlobalReexportMissingAliasTarget.types
@@ -90,7 +90,7 @@ import { JSXInternal } from '..';
 >JSXInternal : any
 
 export function jsx(
->jsx : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild;}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; }
+>jsx : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild;}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -110,7 +110,7 @@ export function jsx(
 
 ): VNode<any>;
 export function jsx<P>(
->jsx : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild;}, key?: string | undefined): VNode<any>; }
+>jsx : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild;}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
@@ -125,7 +125,7 @@ export function jsx<P>(
 ): VNode<any>;
 
 export function jsxs(
->jsxs : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild[];}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; }
+>jsxs : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild[];}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -145,7 +145,7 @@ export function jsxs(
 
 ): VNode<any>;
 export function jsxs<P>(
->jsxs : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild[];}, key?: string | undefined): VNode<any>; }
+>jsxs : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild[];}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
@@ -160,7 +160,7 @@ export function jsxs<P>(
 ): VNode<any>;
 
 export function jsxDEV(
->jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChildren;}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; }
+>jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChildren;}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -180,7 +180,7 @@ export function jsxDEV(
 
 ): VNode<any>;
 export function jsxDEV<P>(
->jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChildren;}, key?: string | undefined): VNode<any>; }
+>jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChildren;}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
diff --git a/tests/baselines/reference/jsxNamespaceImplicitImportJSXNamespace.types b/tests/baselines/reference/jsxNamespaceImplicitImportJSXNamespace.types
index a8d93e63512eb..71651f958b0a3 100644
--- a/tests/baselines/reference/jsxNamespaceImplicitImportJSXNamespace.types
+++ b/tests/baselines/reference/jsxNamespaceImplicitImportJSXNamespace.types
@@ -90,7 +90,7 @@ import { JSXInternal } from '..';
 >JSXInternal : any
 
 export function jsx(
->jsx : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild;}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; }
+>jsx : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild;}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -110,7 +110,7 @@ export function jsx(
 
 ): VNode<any>;
 export function jsx<P>(
->jsx : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild;}, key?: string | undefined): VNode<any>; }
+>jsx : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild;}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
@@ -126,7 +126,7 @@ export function jsx<P>(
 
 
 export function jsxs(
->jsxs : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild[];}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; }
+>jsxs : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChild[];}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -146,7 +146,7 @@ export function jsxs(
 
 ): VNode<any>;
 export function jsxs<P>(
->jsxs : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild[];}, key?: string | undefined): VNode<any>; }
+>jsxs : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChild[] | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChild[];}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
@@ -162,7 +162,7 @@ export function jsxs<P>(
 
 
 export function jsxDEV(
->jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChildren;}, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; }
+>jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes & JSXInternal.SVGAttributes & Record<string, any> & {    children?: ComponentChildren;}, key?: string): VNode<any>; <P>(type: ComponentType<P>, props: P & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; }
 
     type: string,
 >type : string
@@ -182,7 +182,7 @@ export function jsxDEV(
 
 ): VNode<any>;
 export function jsxDEV<P>(
->jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChildren;}, key?: string | undefined): VNode<any>; }
+>jsxDEV : { (type: string, props: JSXInternal.HTMLAttributes<{}> & JSXInternal.SVGAttributes<{}> & Record<string, any> & { children?: ComponentChildren | undefined; }, key?: string | undefined): VNode<any>; <P>(type: ComponentType<P>, props: Attributes & P & {    children?: ComponentChildren;}, key?: string): VNode<any>; }
 
     type: ComponentType<P>,
 >type : ComponentType<P>
diff --git a/tests/baselines/reference/leaveOptionalParameterAsWritten.js b/tests/baselines/reference/leaveOptionalParameterAsWritten.js
new file mode 100644
index 0000000000000..d2a519390a716
--- /dev/null
+++ b/tests/baselines/reference/leaveOptionalParameterAsWritten.js
@@ -0,0 +1,37 @@
+//// [tests/cases/conformance/declarationEmit/leaveOptionalParameterAsWritten.ts] ////
+
+//// [a.ts]
+export interface Foo {}
+
+//// [b.ts]
+import * as a from "./a";
+declare global {
+  namespace teams {
+    export namespace calling {
+      export import Foo = a.Foo;
+    }
+  }
+}
+
+//// [c.ts]
+type Foo = teams.calling.Foo;
+export const bar = (p?: Foo) => {}
+
+
+
+//// [a.d.ts]
+export interface Foo {
+}
+//// [b.d.ts]
+import * as a from "./a";
+declare global {
+    namespace teams {
+        namespace calling {
+            export import Foo = a.Foo;
+        }
+    }
+}
+//// [c.d.ts]
+declare type Foo = teams.calling.Foo;
+export declare const bar: (p?: Foo) => void;
+export {};
diff --git a/tests/baselines/reference/leaveOptionalParameterAsWritten.symbols b/tests/baselines/reference/leaveOptionalParameterAsWritten.symbols
new file mode 100644
index 0000000000000..fbf7d565c51d7
--- /dev/null
+++ b/tests/baselines/reference/leaveOptionalParameterAsWritten.symbols
@@ -0,0 +1,37 @@
+=== tests/cases/conformance/declarationEmit/a.ts ===
+export interface Foo {}
+>Foo : Symbol(Foo, Decl(a.ts, 0, 0))
+
+=== tests/cases/conformance/declarationEmit/b.ts ===
+import * as a from "./a";
+>a : Symbol(a, Decl(b.ts, 0, 6))
+
+declare global {
+>global : Symbol(global, Decl(b.ts, 0, 25))
+
+  namespace teams {
+>teams : Symbol(teams, Decl(b.ts, 1, 16))
+
+    export namespace calling {
+>calling : Symbol(calling, Decl(b.ts, 2, 19))
+
+      export import Foo = a.Foo;
+>Foo : Symbol(Foo, Decl(b.ts, 3, 30))
+>a : Symbol(a, Decl(b.ts, 0, 6))
+>Foo : Symbol(Foo, Decl(a.ts, 0, 0))
+    }
+  }
+}
+
+=== tests/cases/conformance/declarationEmit/c.ts ===
+type Foo = teams.calling.Foo;
+>Foo : Symbol(Foo, Decl(c.ts, 0, 0))
+>teams : Symbol(teams, Decl(b.ts, 1, 16))
+>calling : Symbol(teams.calling, Decl(b.ts, 2, 19))
+>Foo : Symbol(teams.calling.Foo, Decl(b.ts, 3, 30))
+
+export const bar = (p?: Foo) => {}
+>bar : Symbol(bar, Decl(c.ts, 1, 12))
+>p : Symbol(p, Decl(c.ts, 1, 20))
+>Foo : Symbol(Foo, Decl(c.ts, 0, 0))
+
diff --git a/tests/baselines/reference/leaveOptionalParameterAsWritten.types b/tests/baselines/reference/leaveOptionalParameterAsWritten.types
new file mode 100644
index 0000000000000..14632b2b28df4
--- /dev/null
+++ b/tests/baselines/reference/leaveOptionalParameterAsWritten.types
@@ -0,0 +1,35 @@
+=== tests/cases/conformance/declarationEmit/a.ts ===
+export interface Foo {}
+No type information for this code.
+No type information for this code.=== tests/cases/conformance/declarationEmit/b.ts ===
+import * as a from "./a";
+>a : typeof a
+
+declare global {
+>global : typeof global
+
+  namespace teams {
+>teams : typeof teams
+
+    export namespace calling {
+>calling : typeof calling
+
+      export import Foo = a.Foo;
+>Foo : any
+>a : typeof a
+>Foo : Foo
+    }
+  }
+}
+
+=== tests/cases/conformance/declarationEmit/c.ts ===
+type Foo = teams.calling.Foo;
+>Foo : import("tests/cases/conformance/declarationEmit/a").Foo
+>teams : any
+>calling : any
+
+export const bar = (p?: Foo) => {}
+>bar : (p?: Foo) => void
+>(p?: Foo) => {} : (p?: Foo) => void
+>p : import("tests/cases/conformance/declarationEmit/a").Foo | undefined
+
diff --git a/tests/baselines/reference/neverReturningFunctions1.types b/tests/baselines/reference/neverReturningFunctions1.types
index c832fa660dd88..49ec260ad2053 100644
--- a/tests/baselines/reference/neverReturningFunctions1.types
+++ b/tests/baselines/reference/neverReturningFunctions1.types
@@ -1,6 +1,6 @@
 === tests/cases/conformance/controlFlow/neverReturningFunctions1.ts ===
 function fail(message?: string): never {
->fail : (message?: string | undefined) => never
+>fail : (message?: string) => never
 >message : string | undefined
 
     throw new Error(message);
@@ -62,9 +62,9 @@ function f03(x: string) {
 }
 
 function f11(x: string | undefined, fail: (message?: string) => never) {
->f11 : (x: string | undefined, fail: (message?: string | undefined) => never) => void
+>f11 : (x: string | undefined, fail: (message?: string) => never) => void
 >x : string | undefined
->fail : (message?: string | undefined) => never
+>fail : (message?: string) => never
 >message : string | undefined
 
     if (x === undefined) fail("undefined argument");
@@ -82,9 +82,9 @@ function f11(x: string | undefined, fail: (message?: string) => never) {
 }
 
 function f12(x: number, fail: (message?: string) => never): number {
->f12 : (x: number, fail: (message?: string | undefined) => never) => number
+>f12 : (x: number, fail: (message?: string) => never) => number
 >x : number
->fail : (message?: string | undefined) => never
+>fail : (message?: string) => never
 >message : string | undefined
 
     if (x >= 0) return x;
@@ -103,9 +103,9 @@ function f12(x: number, fail: (message?: string) => never): number {
 }
 
 function f13(x: string, fail: (message?: string) => never) {
->f13 : (x: string, fail: (message?: string | undefined) => never) => void
+>f13 : (x: string, fail: (message?: string) => never) => void
 >x : string
->fail : (message?: string | undefined) => never
+>fail : (message?: string) => never
 >message : string | undefined
 
     x;  // string
@@ -123,7 +123,7 @@ namespace Debug {
 >Debug : typeof Debug
 
     export declare function fail(message?: string): never;
->fail : (message?: string | undefined) => never
+>fail : (message?: string) => never
 >message : string | undefined
 }
 
@@ -208,7 +208,7 @@ class Test {
 >Test : Test
 
     fail(message?: string): never {
->fail : (message?: string | undefined) => never
+>fail : (message?: string) => never
 >message : string | undefined
 
         throw new Error(message);
@@ -496,7 +496,7 @@ export interface Component<T extends object = any> {
 >system : any
 
 	init(data?: T): void;
->init : (data?: T | undefined) => void
+>init : (data?: T) => void
 >data : T | undefined
 
 	pause(): void;
diff --git a/tests/baselines/reference/noCrashOnThisTypeUsage.types b/tests/baselines/reference/noCrashOnThisTypeUsage.types
index d0d3048cabf3b..6be36b9174ddd 100644
--- a/tests/baselines/reference/noCrashOnThisTypeUsage.types
+++ b/tests/baselines/reference/noCrashOnThisTypeUsage.types
@@ -5,7 +5,7 @@ interface IListenable {
 >null : null
 
     observe(handler: (change: any, oldValue?: any) => void, fireImmediately?: boolean): void
->observe : (handler: (change: any, oldValue?: any) => void, fireImmediately?: boolean | undefined) => void
+>observe : (handler: (change: any, oldValue?: any) => void, fireImmediately?: boolean) => void
 >handler : (change: any, oldValue?: any) => void
 >change : any
 >oldValue : any
@@ -62,7 +62,7 @@ export class ObservableValue<T> {
 >[] : never[]
 
     observe(handler: (change: any, oldValue?: any) => void, fireImmediately?: boolean) {}
->observe : (handler: (change: any, oldValue?: any) => void, fireImmediately?: boolean | undefined) => void
+>observe : (handler: (change: any, oldValue?: any) => void, fireImmediately?: boolean) => void
 >handler : (change: any, oldValue?: any) => void
 >change : any
 >oldValue : any
diff --git a/tests/baselines/reference/observableInferenceCanBeMade.types b/tests/baselines/reference/observableInferenceCanBeMade.types
index 6931e042adb5b..6bc2aaf43749f 100644
--- a/tests/baselines/reference/observableInferenceCanBeMade.types
+++ b/tests/baselines/reference/observableInferenceCanBeMade.types
@@ -14,7 +14,7 @@ type ObservedValueOf<O> = O extends ObservableInput<infer T> ? T : never;
 
 interface Subscribable<T> {
     subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void): void;
->subscribe : (next?: ((value: T) => void) | undefined, error?: ((error: any) => void) | undefined, complete?: (() => void) | undefined) => void
+>subscribe : (next?: ((value: T) => void) | undefined, error?: ((error: any) => void) | undefined, complete?: () => void) => void
 >next : ((value: T) => void) | undefined
 >value : T
 >error : ((error: any) => void) | undefined
@@ -29,7 +29,7 @@ declare class Observable<T> implements Subscribable<T> {
 >Observable : Observable<T>
 
     subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void): void;
->subscribe : (next?: ((value: T) => void) | undefined, error?: ((error: any) => void) | undefined, complete?: (() => void) | undefined) => void
+>subscribe : (next?: ((value: T) => void) | undefined, error?: ((error: any) => void) | undefined, complete?: () => void) => void
 >next : ((value: T) => void) | undefined
 >value : T
 >error : ((error: any) => void) | undefined
diff --git a/tests/baselines/reference/optionalParameterRetainsNull.types b/tests/baselines/reference/optionalParameterRetainsNull.types
index 94bf71a6f3d42..f1b8f58184195 100644
--- a/tests/baselines/reference/optionalParameterRetainsNull.types
+++ b/tests/baselines/reference/optionalParameterRetainsNull.types
@@ -9,7 +9,7 @@ let a = {
 >{  test<K extends keyof Bar> (a: K,  b?: Bar[K]  |  null)  { }} : { test<K extends keyof Bar>(a: K, b?: Bar[K] | null | undefined): void; }
 
   test<K extends keyof Bar> (a: K,  b?: Bar[K]  |  null)  { }
->test : <K extends keyof Bar>(a: K, b?: Bar[K] | null | undefined) => void
+>test : <K extends keyof Bar>(a: K, b?: Bar[K] | null) => void
 >a : K
 >b : Bar[K] | null | undefined
 >null : null
diff --git a/tests/baselines/reference/primitiveUnionDetection.types b/tests/baselines/reference/primitiveUnionDetection.types
index 03e1ed19884f4..8c9508247c3e9 100644
--- a/tests/baselines/reference/primitiveUnionDetection.types
+++ b/tests/baselines/reference/primitiveUnionDetection.types
@@ -5,7 +5,7 @@ type Kind = "one" | "two" | "three";
 >Kind : "one" | "two" | "three"
 
 declare function getInterfaceFromString<T extends Kind>(options?: { type?: T } & { type?: Kind }): T;
->getInterfaceFromString : <T extends Kind>(options?: ({ type?: T | undefined; } & { type?: Kind | undefined; }) | undefined) => T
+>getInterfaceFromString : <T extends Kind>(options?: {    type?: T;} & {    type?: Kind;}) => T
 >options : ({ type?: T | undefined; } & { type?: Kind | undefined; }) | undefined
 >type : T | undefined
 >type : Kind | undefined
diff --git a/tests/baselines/reference/propertyAccessWidening.types b/tests/baselines/reference/propertyAccessWidening.types
index 244b43be69fce..7185b28f4ca8d 100644
--- a/tests/baselines/reference/propertyAccessWidening.types
+++ b/tests/baselines/reference/propertyAccessWidening.types
@@ -54,7 +54,7 @@ function g2(headerNames: any) {
 // Object in property or element access is widened when target of assignment
 
 function foo(options?: { a: string, b: number }) {
->foo : (options?: { a: string; b: number; } | undefined) => void
+>foo : (options?: {    a: string;    b: number;}) => void
 >options : { a: string; b: number; } | undefined
 >a : string
 >b : number
diff --git a/tests/baselines/reference/spreadIdenticalTypesRemoved.types b/tests/baselines/reference/spreadIdenticalTypesRemoved.types
index 6695770ccc3ed..693b73ef23c4d 100644
--- a/tests/baselines/reference/spreadIdenticalTypesRemoved.types
+++ b/tests/baselines/reference/spreadIdenticalTypesRemoved.types
@@ -17,7 +17,7 @@ interface Animal {
 }
 
 function clonePet(pet: Animal, fullCopy?: boolean) {
->clonePet : (pet: Animal, fullCopy?: boolean | undefined) => { name: string; kind: string; age?: number | undefined; location?: string | undefined; owner?: object | undefined; }
+>clonePet : (pet: Animal, fullCopy?: boolean) => { name: string; kind: string; age?: number | undefined; location?: string | undefined; owner?: object | undefined; }
 >pet : Animal
 >fullCopy : boolean | undefined
 
diff --git a/tests/baselines/reference/spreadUnion3.types b/tests/baselines/reference/spreadUnion3.types
index 62a2fa2da733c..8c4b955ff1a38 100644
--- a/tests/baselines/reference/spreadUnion3.types
+++ b/tests/baselines/reference/spreadUnion3.types
@@ -18,7 +18,7 @@ f(undefined)
 
 
 function g(t?: { a: number } | null): void {
->g : (t?: { a: number; } | null | undefined) => void
+>g : (t?: {    a: number;} | null) => void
 >t : { a: number; } | null | undefined
 >a : number
 >null : null
diff --git a/tests/baselines/reference/stackDepthLimitCastingType.types b/tests/baselines/reference/stackDepthLimitCastingType.types
index 27d09998e3010..76d08fdd570bd 100644
--- a/tests/baselines/reference/stackDepthLimitCastingType.types
+++ b/tests/baselines/reference/stackDepthLimitCastingType.types
@@ -7,7 +7,7 @@ declare global {
 >Model : Model<T, E>
 
         initialize(attributes?: T, options?: CombinedModelConstructorOptions<E, this>): void;
->initialize : (attributes?: T | undefined, options?: CombinedModelConstructorOptions<E, this> | undefined) => void
+>initialize : (attributes?: T, options?: CombinedModelConstructorOptions<E, this>) => void
 >attributes : T | undefined
 >options : CombinedModelConstructorOptions<E, this> | undefined
 
diff --git a/tests/baselines/reference/strictNullLogicalAndOr.types b/tests/baselines/reference/strictNullLogicalAndOr.types
index 33881b5d9d72c..6c6cba3356165 100644
--- a/tests/baselines/reference/strictNullLogicalAndOr.types
+++ b/tests/baselines/reference/strictNullLogicalAndOr.types
@@ -30,7 +30,7 @@ choice(Math.PI);
 >PI : number
 
 function sq(n?: number): number {
->sq : (n?: number | undefined) => number
+>sq : (n?: number) => number
 >n : number | undefined
 
   const r = n !== undefined && n*n || 0;
diff --git a/tests/baselines/reference/substitutionTypesInIndexedAccessTypes.types b/tests/baselines/reference/substitutionTypesInIndexedAccessTypes.types
index a0df1acaa22df..638d2de084c6f 100644
--- a/tests/baselines/reference/substitutionTypesInIndexedAccessTypes.types
+++ b/tests/baselines/reference/substitutionTypesInIndexedAccessTypes.types
@@ -13,11 +13,11 @@ type Subset<T, U> = { [key in keyof T]: key extends keyof U ? T[key] : never };
 >Subset : Subset<T, U>
 
 declare function withBoundary<T extends UserArgs>(args?: Subset<T, UserArgs>): T;
->withBoundary : <T extends UserArgs>(args?: Subset<T, UserArgs> | undefined) => T
+>withBoundary : <T extends UserArgs>(args?: Subset<T, UserArgs>) => T
 >args : Subset<T, UserArgs> | undefined
 
 declare function withoutBoundary<T extends UserArgs>(args?: T): T;
->withoutBoundary : <T extends UserArgs>(args?: T | undefined) => T
+>withoutBoundary : <T extends UserArgs>(args?: T) => T
 >args : T | undefined
 
 const boundaryResult = withBoundary({
diff --git a/tests/baselines/reference/thisTypeInObjectLiterals2.types b/tests/baselines/reference/thisTypeInObjectLiterals2.types
index 3777ded41acaf..bd96bd68bbd1d 100644
--- a/tests/baselines/reference/thisTypeInObjectLiterals2.types
+++ b/tests/baselines/reference/thisTypeInObjectLiterals2.types
@@ -72,7 +72,7 @@ let obj1 = {
 // contextual type.
 
 type Point = {
->Point : { x: number; y: number; z?: number | undefined; moveBy(dx: number, dy: number, dz?: number | undefined): void; }
+>Point : { x: number; y: number; z?: number | undefined; moveBy(dx: number, dy: number, dz?: number): void; }
 
     x: number;
 >x : number
@@ -84,7 +84,7 @@ type Point = {
 >z : number | undefined
 
     moveBy(dx: number, dy: number, dz?: number): void;
->moveBy : (dx: number, dy: number, dz?: number | undefined) => void
+>moveBy : (dx: number, dy: number, dz?: number) => void
 >dx : number
 >dy : number
 >dz : number | undefined
diff --git a/tests/baselines/reference/truthinessCallExpressionCoercion.types b/tests/baselines/reference/truthinessCallExpressionCoercion.types
index 21c2328455c74..16c86086c20e8 100644
--- a/tests/baselines/reference/truthinessCallExpressionCoercion.types
+++ b/tests/baselines/reference/truthinessCallExpressionCoercion.types
@@ -1,6 +1,6 @@
 === tests/cases/compiler/truthinessCallExpressionCoercion.ts ===
 function onlyErrorsWhenTestingNonNullableFunctionType(required: () => boolean, optional?: () => boolean) {
->onlyErrorsWhenTestingNonNullableFunctionType : (required: () => boolean, optional?: (() => boolean) | undefined) => void
+>onlyErrorsWhenTestingNonNullableFunctionType : (required: () => boolean, optional?: () => boolean) => void
 >required : () => boolean
 >optional : (() => boolean) | undefined
 
diff --git a/tests/baselines/reference/truthinessCallExpressionCoercion1.types b/tests/baselines/reference/truthinessCallExpressionCoercion1.types
index cd9f357a5ed4c..7a0aced375dc9 100644
--- a/tests/baselines/reference/truthinessCallExpressionCoercion1.types
+++ b/tests/baselines/reference/truthinessCallExpressionCoercion1.types
@@ -1,6 +1,6 @@
 === tests/cases/compiler/truthinessCallExpressionCoercion1.ts ===
 function onlyErrorsWhenTestingNonNullableFunctionType(required: () => boolean, optional?: () => boolean) {
->onlyErrorsWhenTestingNonNullableFunctionType : (required: () => boolean, optional?: (() => boolean) | undefined) => void
+>onlyErrorsWhenTestingNonNullableFunctionType : (required: () => boolean, optional?: () => boolean) => void
 >required : () => boolean
 >optional : (() => boolean) | undefined
 
diff --git a/tests/baselines/reference/truthinessCallExpressionCoercion2.types b/tests/baselines/reference/truthinessCallExpressionCoercion2.types
index 85eeacc46f731..96f115a621d09 100644
--- a/tests/baselines/reference/truthinessCallExpressionCoercion2.types
+++ b/tests/baselines/reference/truthinessCallExpressionCoercion2.types
@@ -14,7 +14,7 @@ declare class B {
 }
 
 function test(required1: () => boolean, required2: () => boolean, b: boolean, optional?: () => boolean) {
->test : (required1: () => boolean, required2: () => boolean, b: boolean, optional?: (() => boolean) | undefined) => void
+>test : (required1: () => boolean, required2: () => boolean, b: boolean, optional?: () => boolean) => void
 >required1 : () => boolean
 >required2 : () => boolean
 >b : boolean
diff --git a/tests/baselines/reference/unionReductionMutualSubtypes.types b/tests/baselines/reference/unionReductionMutualSubtypes.types
index 748826d08f6c9..0cd09be38a6db 100644
--- a/tests/baselines/reference/unionReductionMutualSubtypes.types
+++ b/tests/baselines/reference/unionReductionMutualSubtypes.types
@@ -15,9 +15,9 @@ declare const val: ReturnVal;
 >val : ReturnVal
 
 function run(options: { something?(b?: string): void }) {
->run : (options: { something?(b?: string | undefined): void; }) => void
->options : { something?(b?: string | undefined): void; }
->something : ((b?: string | undefined) => void) | undefined
+>run : (options: { something?(b?: string): void; }) => void
+>options : { something?(b?: string): void; }
+>something : ((b?: string) => void) | undefined
 >b : string | undefined
 
     const something = options.something ?? val.something;
diff --git a/tests/baselines/reference/unionTypeReduction2.types b/tests/baselines/reference/unionTypeReduction2.types
index f4f724e6dcdb0..7c79aab4ddfb9 100644
--- a/tests/baselines/reference/unionTypeReduction2.types
+++ b/tests/baselines/reference/unionTypeReduction2.types
@@ -1,10 +1,10 @@
 === tests/cases/conformance/types/union/unionTypeReduction2.ts ===
 function f1(x: { f(): void }, y: { f(x?: string): void }) {
->f1 : (x: {    f(): void;}, y: { f(x?: string | undefined): void; }) => void
+>f1 : (x: {    f(): void;}, y: { f(x?: string): void; }) => void
 >x : { f(): void; }
 >f : () => void
->y : { f(x?: string | undefined): void; }
->f : (x?: string | undefined) => void
+>y : { f(x?: string): void; }
+>f : (x?: string) => void
 >x : string | undefined
 
     let z = !!true ? x : y;  // { f(x?: string): void }
@@ -31,12 +31,12 @@ function f1(x: { f(): void }, y: { f(x?: string): void }) {
 }
 
 function f2(x: { f(x: string | undefined): void }, y: { f(x?: string): void }) {
->f2 : (x: { f(x: string | undefined): void; }, y: { f(x?: string | undefined): void; }) => void
+>f2 : (x: { f(x: string | undefined): void; }, y: { f(x?: string): void; }) => void
 >x : { f(x: string | undefined): void; }
 >f : (x: string | undefined) => void
 >x : string | undefined
->y : { f(x?: string | undefined): void; }
->f : (x?: string | undefined) => void
+>y : { f(x?: string): void; }
+>f : (x?: string) => void
 >x : string | undefined
 
     let z = !!true ? x : y;  // { f(x?: string): void }
@@ -63,9 +63,9 @@ function f2(x: { f(x: string | undefined): void }, y: { f(x?: string): void }) {
 }
 
 function f3(x: () => void, y: (x?: string) => void) {
->f3 : (x: () => void, y: (x?: string | undefined) => void) => void
+>f3 : (x: () => void, y: (x?: string) => void) => void
 >x : () => void
->y : (x?: string | undefined) => void
+>y : (x?: string) => void
 >x : string | undefined
 
     let f = !!true ? x : y;  // (x?: string) => void
@@ -88,10 +88,10 @@ function f3(x: () => void, y: (x?: string) => void) {
 }
 
 function f4(x: (x: string | undefined) => void, y: (x?: string) => void) {
->f4 : (x: (x: string | undefined) => void, y: (x?: string | undefined) => void) => void
+>f4 : (x: (x: string | undefined) => void, y: (x?: string) => void) => void
 >x : (x: string | undefined) => void
 >x : string | undefined
->y : (x?: string | undefined) => void
+>y : (x?: string) => void
 >x : string | undefined
 
     let f = !!true ? x : y;  // (x?: string) => void
@@ -114,10 +114,10 @@ function f4(x: (x: string | undefined) => void, y: (x?: string) => void) {
 }
 
 function f5(x: (x: string | undefined) => void, y: (x?: 'hello') => void) {
->f5 : (x: (x: string | undefined) => void, y: (x?: "hello" | undefined) => void) => void
+>f5 : (x: (x: string | undefined) => void, y: (x?: 'hello') => void) => void
 >x : (x: string | undefined) => void
 >x : string | undefined
->y : (x?: "hello" | undefined) => void
+>y : (x?: 'hello') => void
 >x : "hello" | undefined
 
     let f = !!true ? x : y;  // (x?: 'hello') => void
@@ -140,10 +140,10 @@ function f5(x: (x: string | undefined) => void, y: (x?: 'hello') => void) {
 }
 
 function f6(x: (x: 'hello' | undefined) => void, y: (x?: string) => void) {
->f6 : (x: (x: 'hello' | undefined) => void, y: (x?: string | undefined) => void) => void
+>f6 : (x: (x: 'hello' | undefined) => void, y: (x?: string) => void) => void
 >x : (x: 'hello' | undefined) => void
 >x : "hello" | undefined
->y : (x?: string | undefined) => void
+>y : (x?: string) => void
 >x : string | undefined
 
     let f = !!true ? x : y;  // (x: 'hello' | undefined) => void
@@ -173,10 +173,10 @@ type A = {
 }
 
 type B = {
->B : { f(x?: string | undefined): void; g(): void; }
+>B : { f(x?: string): void; g(): void; }
 
     f(x?: string): void;
->f : (x?: string | undefined) => void
+>f : (x?: string) => void
 >x : string | undefined
 
     g(): void;
@@ -227,9 +227,9 @@ declare const val: ReturnVal;
 >val : ReturnVal
 
 function run(options: { something?(b?: string): void }) {
->run : (options: { something?(b?: string | undefined): void; }) => void
->options : { something?(b?: string | undefined): void; }
->something : ((b?: string | undefined) => void) | undefined
+>run : (options: { something?(b?: string): void; }) => void
+>options : { something?(b?: string): void; }
+>something : ((b?: string) => void) | undefined
 >b : string | undefined
 
     const something = options.something ?? val.something;
diff --git a/tests/baselines/reference/variadicTuples1.types b/tests/baselines/reference/variadicTuples1.types
index 3aa03e67b84b9..64a25d510c047 100644
--- a/tests/baselines/reference/variadicTuples1.types
+++ b/tests/baselines/reference/variadicTuples1.types
@@ -1349,13 +1349,13 @@ const b = a.bind("", 1);  // Desc<[boolean], object>
 // Repro from #39607
 
 declare function getUser(id: string, options?: { x?: string }): string;
->getUser : (id: string, options?: { x?: string | undefined; } | undefined) => string
+>getUser : (id: string, options?: {    x?: string;}) => string
 >id : string
 >options : { x?: string | undefined; } | undefined
 >x : string | undefined
 
 declare function getOrgUser(id: string, orgId: number, options?: { y?: number, z?: boolean }): void;
->getOrgUser : (id: string, orgId: number, options?: { y?: number | undefined; z?: boolean | undefined; } | undefined) => void
+>getOrgUser : (id: string, orgId: number, options?: {    y?: number;    z?: boolean;}) => void
 >id : string
 >orgId : number
 >options : { y?: number | undefined; z?: boolean | undefined; } | undefined
diff --git a/tests/cases/conformance/declarationEmit/leaveOptionalParameterAsWritten.ts b/tests/cases/conformance/declarationEmit/leaveOptionalParameterAsWritten.ts
new file mode 100644
index 0000000000000..f22262cb82c11
--- /dev/null
+++ b/tests/cases/conformance/declarationEmit/leaveOptionalParameterAsWritten.ts
@@ -0,0 +1,22 @@
+// @module: esnext
+// @outDir: dist
+// @declaration: true
+// @emitDeclarationOnly: true
+// @strictNullChecks: true
+
+// @Filename: a.ts
+export interface Foo {}
+
+// @Filename: b.ts
+import * as a from "./a";
+declare global {
+  namespace teams {
+    export namespace calling {
+      export import Foo = a.Foo;
+    }
+  }
+}
+
+// @Filename: c.ts
+type Foo = teams.calling.Foo;
+export const bar = (p?: Foo) => {}
\ No newline at end of file