diff --git a/lib/Factory.js b/lib/Factory.js
index 0d1b658..84543f0 100644
--- a/lib/Factory.js
+++ b/lib/Factory.js
@@ -79,6 +79,7 @@ Factory.prototype._create_control = function(value) {
 };
 
 Factory.prototype._map_list = function(list, func) {
+    "use strict";
     var output_list = {};
 
     Object.keys(list).forEach( function(entry) {