diff --git a/lib/ace/worker/worker.js b/lib/ace/worker/worker.js
index 04f43a04..ad7b4aaf 100644
--- a/lib/ace/worker/worker.js
+++ b/lib/ace/worker/worker.js
@@ -105,7 +105,7 @@ onmessage = function(e) {
         var clazz = require(msg.module)[msg.classname];
         main = new clazz(sender);
     } 
-    else if (msg.event) {
+    else if (msg.event && sender) {
         sender._dispatchEvent(msg.event, msg.data);
     }
 };
\ No newline at end of file