diff --git a/lib/javascript-static.js b/lib/javascript-static.js
index dc56fe35d18..5cd262a9dbc 100644
--- a/lib/javascript-static.js
+++ b/lib/javascript-static.js
@@ -1322,8 +1322,9 @@ function updateProgressBar(id, percent, msg, estimate) {
         if (!(exception instanceof TypeError)) {
             throw exception;
         }
-        event = document.createEvent('Event');
+        event = document.createEvent('CustomEvent');
         event.initCustomEvent('update', false, true, eventData);
+        event.prototype = window.Event.prototype;
     }
 
     el.dispatchEvent(event);