diff --git a/apns.py b/apns.py
index 826135f..620869e 100644
--- a/apns.py
+++ b/apns.py
@@ -557,7 +557,7 @@ def _make_sure_error_response_handler_worker_alive(self):
 
     def send_notification_multiple(self, frame):
         self._sent_notifications += frame.get_notifications(self)
-        return self.write(frame.get_frame())
+        return self.write(bytes(frame.get_frame()))
     
     def register_response_listener(self, response_listener):
         self._response_listener = response_listener