diff --git a/addons/calendar/models/calendar_event.py b/addons/calendar/models/calendar_event.py
index 183bac695933e..8ad88f2b3edfc 100644
--- a/addons/calendar/models/calendar_event.py
+++ b/addons/calendar/models/calendar_event.py
@@ -1110,7 +1110,7 @@ def ics_datetime(idate, allday=False):
                         delta = timedelta(hours=duration)
                     elif interval == 'minutes':
                         delta = timedelta(minutes=duration)
-                    trigger.value = delta
+                    trigger.value = -delta
                     valarm.add('DESCRIPTION').value = alarm.name or u'Odoo'
             for attendee in meeting.attendee_ids:
                 attendee_add = event.add('attendee')