diff --git a/ember/ember.d.ts b/ember/ember.d.ts
index 80be5d04d9..40d2f9859d 100644
--- a/ember/ember.d.ts
+++ b/ember/ember.d.ts
@@ -992,7 +992,7 @@ declare module Ember {
             yield(options?: {}): string;
         }
         function precompile(string: string): void;
-        function registerBoundHelper(name: string, func: Function, dependentKeys: string): void;
+        function registerBoundHelper(name: string, func: Function, dependentKeys?: string): void;
         class Compiler { }
         class JavaScriptCompiler { }
         function registerHelper(name: string, fn: Function, inverse?: boolean): void;