diff --git a/addons/base_calendar/base_calendar.py b/addons/base_calendar/base_calendar.py
index 5bc12c69671..7871cca7a3a 100644
--- a/addons/base_calendar/base_calendar.py
+++ b/addons/base_calendar/base_calendar.py
@@ -1416,6 +1416,15 @@ e.g.: Every other month on the last Sunday of the month for 10 occurrences:\
         @param context: A standard dictionary for contextual values
         @return: True
         """        
+        #removing useless value
+        old_vals = self.read(cr, uid, ids[0], ['rrule'], context)
+        if not old_vals:
+            old_vals = {}
+        if not 'rrule' in old_vals:
+            old_vals["rrule"] = ""
+        if 'rrule' in vals and not vals['rrule'] and not old_vals['rrule']: 
+            del vals['rrule']
+        
         if context is None:
             context = {}
         if isinstance(ids, (str, int, long)):