diff --git a/addons/base_calendar/base_calendar.py b/addons/base_calendar/base_calendar.py
index 9db200e7b77..30bc83e0616 100644
--- a/addons/base_calendar/base_calendar.py
+++ b/addons/base_calendar/base_calendar.py
@@ -923,6 +923,10 @@ class calendar_event(osv.osv):
                 if datas.get('rrule_type') == 'none':
                     result[event] = False
                 elif datas.get('rrule_type') == 'custom':
+                    if datas.get('interval', 0) < 0:
+                        raise osv.except_osv('Warning!', 'Interval can not be Negative')
+                    if datas.get('count', 0) < 0:
+                        raise osv.except_osv('Warning!', 'Count can not be Negative')
                     rrule_custom = self.compute_rule_string(cr, uid, datas,\
                                                          context=context)
                     result[event] = rrule_custom