diff --git a/addStyles.js b/addStyles.js
index ef4fd5f..8d45277 100644
--- a/addStyles.js
+++ b/addStyles.js
@@ -11,7 +11,7 @@ var stylesInDom = {},
 		};
 	},
 	isOldIE = memoize(function() {
-		return /msie [6-9]\b/.test(window.navigator.userAgent.toLowerCase());
+		return /msie [6-9]\b/.test(self.navigator.userAgent.toLowerCase());
 	}),
 	getHeadElement = memoize(function () {
 		return document.head || document.getElementsByTagName("head")[0];