diff --git a/src/index.js b/src/index.js
index b9b4a76..b1083d6 100644
--- a/src/index.js
+++ b/src/index.js
@@ -13,7 +13,7 @@ const protectedproperties = (() => {
 
   return Object
     .getOwnPropertyNames(window)
-    .filter(prop => global[prop]);
+    .filter(prop => typeof global[prop] !== 'undefined');
 })();
 
 module.exports = (...args) => {