diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index 1be8d331a6ff7..292d0d2f6c9b0 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -238,7 +238,7 @@ interface ObjectConstructor {
      * Returns the names of the enumerable string properties and methods of an object.
      * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
      */
-    keys(o: object): string[];
+    keys<T extends object>(o: T): Array<Extract<keyof T, string>>;
 }
 
 /**