diff --git a/src/external_app/external_messaging.ts b/src/external_app/external_messaging.ts
index 7d2cbc1b34e4..47b334ce038e 100644
--- a/src/external_app/external_messaging.ts
+++ b/src/external_app/external_messaging.ts
@@ -104,7 +104,7 @@ export class ExternalMessaging {
     }
     if (window.externalApp) {
       window.externalApp.externalBus(JSON.stringify(msg));
-    } else {
+    } else if (window.webkit) {
       window.webkit!.messageHandlers.externalBus.postMessage(msg);
     }
   }