diff --git a/async/async.d.ts b/async/async.d.ts
index 5ba56e0db..12aa4123f 100644
--- a/async/async.d.ts
+++ b/async/async.d.ts
@@ -13,7 +13,7 @@ interface AsyncWorker<T> { (task: T, callback: Function): void; }
 interface AsyncQueue<T> {
     length(): number;
     concurrency: number;
-    push(task: T, callback: AsyncMultipleResultsCallback<T>): void;
+    push(task: T, callback?: AsyncMultipleResultsCallback<T>): void;
     saturated: AsyncMultipleResultsCallback<T>;
     empty: AsyncMultipleResultsCallback<T>;
     drain: AsyncMultipleResultsCallback<T>;
@@ -79,4 +79,4 @@ declare var async: Async;
 
 declare module "async" {
 	export = async;
-}
\ No newline at end of file
+}