diff --git a/angucomplete-alt.js b/angucomplete-alt.js
index 6fb8d005..f95a8f7d 100644
--- a/angucomplete-alt.js
+++ b/angucomplete-alt.js
@@ -8,6 +8,7 @@
 /*! Copyright (c) 2014 Hidenari Nozaki and contributors | Licensed under the MIT license */
 
 (function (root, factory) {
+  'use strict';
   if (typeof module !== 'undefined' && module.exports) {
     // CommonJS
     module.exports = factory(require('angular'));