diff --git a/async/async.d.ts b/async/async.d.ts
index 6054e9a478..418f5539b3 100644
--- a/async/async.d.ts
+++ b/async/async.d.ts
@@ -76,11 +76,11 @@ interface Async {
     each<T>(arr: T[], iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
     eachSeries<T>(arr: T[], iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
     eachLimit<T>(arr: T[], limit: number, iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
-    forEachOf(obj: any, iterator: (item: any, key: [string|number], callback?: ErrorCallback) => void, callback: ErrorCallback): void;
+    forEachOf(obj: any, iterator: (item: any, key: string|number, callback?: ErrorCallback) => void, callback: ErrorCallback): void;
     forEachOf<T>(obj: T[], iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
-    forEachOfSeries(obj: any, iterator: (item: any, key: [string|number], callback?: ErrorCallback) => void, callback: ErrorCallback): void;
+    forEachOfSeries(obj: any, iterator: (item: any, key: string|number, callback?: ErrorCallback) => void, callback: ErrorCallback): void;
     forEachOfSeries<T>(obj: T[], iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
-    forEachOfLimit(obj: any, limit: number, iterator: (item: any, key: [string|number], callback?: ErrorCallback) => void, callback: ErrorCallback): void;
+    forEachOfLimit(obj: any, limit: number, iterator: (item: any, key: string|number, callback?: ErrorCallback) => void, callback: ErrorCallback): void;
     forEachOfLimit<T>(obj: T[], limit: number, iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
     map<T, R>(arr: T[], iterator: AsyncResultIterator<T, R>, callback?: AsyncResultArrayCallback<R>): any;
     mapSeries<T, R>(arr: T[], iterator: AsyncResultIterator<T, R>, callback?: AsyncResultArrayCallback<R>): any;