diff --git a/addons/calendar/controllers/bus.py b/addons/calendar/controllers/bus.py
index 90203db4463..4ed07ebba9e 100644
--- a/addons/calendar/controllers/bus.py
+++ b/addons/calendar/controllers/bus.py
@@ -10,5 +10,6 @@ class CalendarBusController(BusController):
     # --------------------------
     def _poll(self, dbname, channels, last, options):
         if request.session.uid:
+            channels = list(channels)
             channels.append((request.db, 'calendar.alarm', request.env.user.partner_id.id))
         return super(CalendarBusController, self)._poll(dbname, channels, last, options)