diff --git a/sinon/sinon.d.ts b/sinon/sinon.d.ts
index cdb316976..fec30d70d 100644
--- a/sinon/sinon.d.ts
+++ b/sinon/sinon.d.ts
@@ -264,6 +264,7 @@ declare module Sinon {
         fakeHTTPMethods: boolean;
         getHTTPMethod: (request: SinonFakeXMLHttpRequest) => string;
         requests: SinonFakeXMLHttpRequest[];
+        respondImmediately: boolean;
 
         // Methods
         respondWith(body: string): void;