diff --git a/jquery/jquery-1.8.d.ts b/jquery/jquery-1.8.d.ts
index 88dd976ca8..76e14c58b6 100644
--- a/jquery/jquery-1.8.d.ts
+++ b/jquery/jquery-1.8.d.ts
@@ -179,7 +179,7 @@ interface JQueryStatic {
 
     ajaxSettings: JQueryAjaxSettings;
 
-    ajaxSetup(options: any);
+    ajaxSetup(options?: any);
 
     get(url: string, data?: any, success?: any, dataType?: any): JQueryXHR;
     getJSON(url: string, data?: any, success?: any): JQueryXHR;