diff --git a/IPython/frontend/html/notebook/static/js/notificationwidget.js b/IPython/frontend/html/notebook/static/js/notificationwidget.js
index 892cedcb9..a6626de5c 100644
--- a/IPython/frontend/html/notebook/static/js/notificationwidget.js
+++ b/IPython/frontend/html/notebook/static/js/notificationwidget.js
@@ -10,7 +10,7 @@
 //============================================================================
 
 var IPython = (function (IPython) {
-
+    "use strict";
     var utils = IPython.utils;