diff --git a/request-promise/request-promise.d.ts b/request-promise/request-promise.d.ts
index 7a94ce596..1832787be 100644
--- a/request-promise/request-promise.d.ts
+++ b/request-promise/request-promise.d.ts
@@ -13,7 +13,7 @@ declare module 'request-promise' {
 	import http = require('http');
         
     interface RequestPromise extends request.Request {
-        then(onFulfilled: Function, onRejected: Function): Promise<any>;
+        then(onFulfilled: Function, onRejected?: Function): Promise<any>;
         catch(onRejected: Function): Promise<any>;
         finally(onFinished: Function): Promise<any>;
         promise(): Promise<any>;