diff --git a/src/document.js b/src/document.js
index 523b915db..d9bf52d6f 100644
--- a/src/document.js
+++ b/src/document.js
@@ -456,6 +456,10 @@ function setupWindow(window, args) {
     event.initMessageEvent('message', false, false, data, eventOrigin, null, source, []);
 
     this.dispatchEvent(event);
+
+    const handled = browser.emit('message', data);
+    if (!handled)
+      browser.log('Unhandled message("%s")');
   };
 
   // Inject HTMLDocument.hasFocus function