diff --git a/javascript/jsapi/window.bnd b/javascript/jsapi/window.bnd
index 7ad54dbac..56b2ff090 100644
--- a/javascript/jsapi/window.bnd
+++ b/javascript/jsapi/window.bnd
@@ -246,7 +246,7 @@ operation dispatchEvent %{
 				JS_GetProperty(cx, JSAPI_THIS_OBJECT(cx, vp), "onload", &eventval);
 			}
 
-			if (JSVAL_IS_VOID(eventval)) {
+			if (!JSVAL_IS_VOID(eventval)) {
 				event_argv[0] = eventval;
 				jsret = JS_CallFunctionValue(cx, NULL, eventval, 1, event_argv, &event_rval);
 			}