diff --git a/src/output/srcdoc.html b/src/output/srcdoc.html
index 3948a54a..6d774f1c 100644
--- a/src/output/srcdoc.html
+++ b/src/output/srcdoc.html
@@ -122,7 +122,7 @@
 				}
 
 				window.addEventListener("unhandledrejection", event => {
-					if (event.reason.message.includes('Cross-origin')) {
+					if (event.reason.message && event.reason.message.includes('Cross-origin')) {
 						event.preventDefault()
 						return
 					}