diff --git a/common/content/util.js b/common/content/util.js
index 94d9fd3c..2f92ae2e 100644
--- a/common/content/util.js
+++ b/common/content/util.js
@@ -716,7 +716,7 @@ util.Array = function Array_(ary) {
                 return util.Array(res);
             return res;
         },
-        concat: function() Array.concat.apply(this.__proto__, arguments),
+        concat: function() [].concat.apply(this.__proto__, arguments),
         map: function() this.__noSuchMethod__("map", Array.slice(arguments)),
     };
     return obj;