Index: lib/messaging.js
===================================================================
--- a/lib/messaging.js
+++ b/lib/messaging.js
@@ -37,29 +37,26 @@
   _onMessage: function(message, sender, sendResponse)
   {
     let async = false;
-    let callbacks = this._eventEmitter._listeners[message.type];
+    let callbacks = this._eventEmitter.listeners(message.type);
 
-    if (callbacks)
+    for (let callback of callbacks)
     {
-      for (let callback of callbacks)
+      let response = callback(message, sender);
+
+      if (response && typeof response.then == "function")
       {
-        let response = callback(message, sender);
-
-        if (response && typeof response.then == "function")
-        {
-          response.then(
-            sendResponse,
-            reason => {
-              console.error(reason);
-              sendResponse(undefined);
-            }
-          );
-          async = true;
-        }
-        else if (typeof response != "undefined")
-        {
-          sendResponse(response);
-        }
+        response.then(
+          sendResponse,
+          reason => {
+            console.error(reason);
+            sendResponse(undefined);
+          }
+        );
+        async = true;
+      }
+      else if (typeof response != "undefined")
+      {
+        sendResponse(response);
       }
     }