diff --git a/src/core.js b/src/core.js
index d268b34..a4193df 100644
--- a/src/core.js
+++ b/src/core.js
@@ -32,8 +32,8 @@
         * prefix.js: addresses prefixed APIs present in global and non-Element contexts
     */
     prefix = (function () {
-      var keys = Object.keys(window).join();
-      var pre = ((keys.match(/,(ms)/) || keys.match(/,(moz)/) || keys.match(/,(O)/)) || [null, 'webkit'])[1].toLowerCase();
+      var keys = Object.keys(Object.getPrototypeOf(window)).concat(Object.keys(window)).join();
+      var pre = (keys.match(/,(ms|moz|O)/) || [null, 'webkit'])[1].toLowerCase();
       return {
         dom: pre == 'ms' ? 'MS' : pre,
         lowercase: pre,