diff --git a/q/Q.d.ts b/q/Q.d.ts
index 044f9752f..15f3fdea7 100644
--- a/q/Q.d.ts
+++ b/q/Q.d.ts
@@ -36,7 +36,7 @@ interface Qpromise {
 }
 
 interface QStatic {
-    when(value: any, onFulfilled: Function, onRejected?: Function): Qpromise;
+    when(value: any, onFulfilled?: Function, onRejected?: Function): Qpromise;
     try(method: Function, ...args: any[]): Qpromise;
     fbind(method: Function, ...args: any[]): Qpromise;
     fcall(method: Function, ...args: any[]): Qpromise;