diff --git a/README.md b/README.md
index 822bcf1c..af6c683a 100644
--- a/README.md
+++ b/README.md
@@ -74,7 +74,7 @@ And nested ones, too.
 | `Date`     | `string` via `toISOString()` |
 | `RegExp`   | `string`                                    |
 
-#### Required 
+#### Required
 You can set specific fields of an object as `required` in your schema, by adding `required: true` inside the key properties.  
 Example:
 ```javascript
@@ -94,6 +94,31 @@ const schema = {
 ```
 If the object to stringify has not the required field(s), `fast-json-stringify` will throw an error.
 
+#### Missing fields
+If a field *is present* in the schema (and is not required) but it *is not present* in the object to stringify, `fast-json-stringify` will not write it in the final string.  
+Example:
+```javascript
+const stringify = fastJson({
+  title: 'Example Schema',
+  type: 'object',
+  properties: {
+    nickname: {
+      type: 'string'
+    },
+    mail: {
+      type: 'string',
+      required: true
+    }
+  }
+})
+
+const obj = {
+  mail: 'mail@example.com'
+}
+
+console.log(stringify(obj)) // '{"mail":"mail@example.com"}'
+```
+
 ## Acknowledgements
 
 This project was kindly sponsored by [nearForm](http://nearform.com).
diff --git a/index.js b/index.js
index 3df51134..bc92ca87 100644
--- a/index.js
+++ b/index.js
@@ -140,9 +140,12 @@ function buildObject (schema, code, name) {
   var laterCode = ''
 
   Object.keys(schema.properties).forEach((key, i, a) => {
+    // Using obj.key !== undefined instead of obj.hasOwnProperty(prop) for perf reasons,
+    // see https://github.com/mcollina/fast-json-stringify/pull/3 for discussion.
     code += `
-      json += '${$asString(key)}:'
-    `
+      if (obj.${key} !== undefined) {
+        json += '${$asString(key)}:'
+      `
 
     const result = nested(laterCode, name, '.' + key, schema.properties[key])
 
@@ -150,8 +153,21 @@ function buildObject (schema, code, name) {
     laterCode = result.laterCode
 
     if (i < a.length - 1) {
-      code += 'json += \',\''
+      code += `
+        json += \',\'
+      `
+    }
+
+    if (schema.properties[key].required) {
+      code += `
+      } else {
+        throw new Error('${key} is required!')
+      `
     }
+
+    code += `
+      }
+    `
   })
 
   code += `
@@ -202,12 +218,6 @@ function buildArray (schema, code, name) {
 function nested (laterCode, name, key, schema) {
   var code = ''
   var funcName
-  if (schema.required) {
-    code += `
-      if (!obj.hasOwnProperty('${key.slice(1)}')) {
-        throw new Error('${key} is required!')
-      }`
-  }
   const type = schema.type
   switch (type) {
     case 'null':
diff --git a/test.js b/test.js
index a69d5ee5..69edd878 100644
--- a/test.js
+++ b/test.js
@@ -288,7 +288,31 @@ test('object with required field', (t) => {
     })
     t.fail()
   } catch (e) {
-    t.is(e.message, '.str is required!')
+    t.is(e.message, 'str is required!')
     t.pass()
   }
 })
+
+test('missing values', (t) => {
+  t.plan(3)
+
+  const stringify = build({
+    title: 'object with missing values',
+    type: 'object',
+    properties: {
+      str: {
+        type: 'string'
+      },
+      num: {
+        type: 'number'
+      },
+      val: {
+        type: 'string'
+      }
+    }
+  })
+
+  t.equal('{"val":"value"}', stringify({ val: 'value' }))
+  t.equal('{"str":"string","val":"value"}', stringify({ str: 'string', val: 'value' }))
+  t.equal('{"str":"string","num":42,"val":"value"}', stringify({ str: 'string', num: 42, val: 'value' }))
+})