diff --git a/src/js/contentscript-end.js b/src/js/contentscript-end.js
index 7f8f1b7ad..04d62901f 100644
--- a/src/js/contentscript-end.js
+++ b/src/js/contentscript-end.js
@@ -80,7 +80,7 @@ var messager = vAPI.messaging.channel('contentscript-end.js');
         // to force them to be seen as "already injected".
         selectors = vAPI.donthideCosmeticFilters;
         if ( typeof selectors === 'object' ) {
-            for ( selector in selectors ) {
+            for ( var selector in selectors ) {
                 if ( selectors.hasOwnProperty(selector) ) {
                     injectedSelectors[selector] = true;
                 }