diff --git a/lib/preload.js b/lib/preload.js
index aff8448b..c55b76ea 100644
--- a/lib/preload.js
+++ b/lib/preload.js
@@ -52,7 +52,7 @@ Object.defineProperties(window, {
   },
   onbeforeunload: {
     enumerable: true,
-    writable: false,
+    writable: true,
     value: null
   }
 })