diff --git a/web/js/codeworld.js b/web/js/codeworld.js
index ecb95885..e4a5a904 100644
--- a/web/js/codeworld.js
+++ b/web/js/codeworld.js
@@ -334,7 +334,7 @@ function initCodeworld() {
     lineNumbers: true,
     autofocus: true,
     matchBrackets: true,
-    styleActiveLine: !WURFL || !WURFL.is_mobile,
+    styleActiveLine: !window.WURFL || !window.WURFL.is_mobile,
     showTrailingSpace: true,
     indentWithTabs: false,
     indentUnit: 2,