diff --git a/libraries/fetch-polyfill.js b/libraries/fetch-polyfill.js
index 9dd417d..9c2e526 100644
--- a/libraries/fetch-polyfill.js
+++ b/libraries/fetch-polyfill.js
@@ -456,7 +456,7 @@
       }
 
       const xhr = new XMLHttpRequest();
-      const isAsync = !(init.keepalive || false);
+      const isAsync = !(init?.keepalive ?? false);
 
       if (isAsync) {
         function abortXhr() {