diff --git a/src/lib/es2015.iterable.d.ts b/src/lib/es2015.iterable.d.ts
index b679bea14d5..faba45bc518 100644
--- a/src/lib/es2015.iterable.d.ts
+++ b/src/lib/es2015.iterable.d.ts
@@ -177,7 +177,7 @@ interface ReadonlySet<T> {
 }
 
 interface SetConstructor {
-    new <T>(iterable: Iterable<T>): Set<T>;
+    new <T>(iterable?: Iterable<T> | null): Set<T>;
 }
 
 interface WeakSet<T extends object> { }