diff --git a/src/ch04/exercises.ts b/src/ch04/exercises.ts
index 9cb666a..fe37251 100644
--- a/src/ch04/exercises.ts
+++ b/src/ch04/exercises.ts
@@ -86,6 +86,6 @@ is(10, 'foo') // Error TS2345: Argument of type '"foo"' is not assignable
 // [Hard] I should be able to pass any number of arguments
 is([1], [1, 2], [1, 2, 3]) // false
 
-function is<T>(a: T, ...b: [T, ...T[]]): boolean {
+function is<T>(a: T, ...b: [...T[]]): boolean {
   return b.every(_ => _ === a)
 }