diff --git a/channel-messaging-basic/page2.html b/channel-messaging-basic/page2.html
index 3929fec5..d5d36c11 100644
--- a/channel-messaging-basic/page2.html
+++ b/channel-messaging-basic/page2.html
@@ -14,6 +14,8 @@
       window.addEventListener("message", onMessage);
 
       function onMessage(e) {
+        if (!e.ports) return;
+
         output.innerHTML = e.data;
         // Use the transfered port to post a message back to the main frame
         e.ports[0].postMessage("Message back from the IFrame");