diff --git a/js/h5p-content-upgrade-worker.js b/js/h5p-content-upgrade-worker.js
index 44b6949..26ad038 100644
--- a/js/h5p-content-upgrade-worker.js
+++ b/js/h5p-content-upgrade-worker.js
@@ -1,4 +1,4 @@
-var H5P = window.H5P = window.H5P || {};
+var H5P = H5P || {};
 importScripts('h5p-version.js', 'h5p-content-upgrade-process.js');
 
 var libraryLoadedCallback;