diff --git a/js/impress.js b/js/impress.js
index 231609d87..c96f91be1 100644
--- a/js/impress.js
+++ b/js/impress.js
@@ -10,6 +10,7 @@
  */
 
 (function ( document, window ) {
+    'use strict';
 
     // HELPER FUNCTIONS