diff --git a/addons/calendar/views/calendar_views.xml b/addons/calendar/views/calendar_views.xml
index 03432741965..6a5c11de816 100644
--- a/addons/calendar/views/calendar_views.xml
+++ b/addons/calendar/views/calendar_views.xml
@@ -116,10 +116,10 @@
                                     <field name="stop" attrs="{'invisible': True}"/>
                                     <field name="id" attrs="{'invisible': True}"/>
 
-                                    <field name="start_date" string="Starting at" attrs="{'invisible': [('allday','=',False)], 'readonly': [('id', '!=', False), ('recurrency','=',True)]}"/>
-                                    <field name="stop_date" string="Ending at" attrs="{'invisible': [('allday','=',False)], 'readonly': [('id', '!=', False), ('recurrency','=',True)]}"/>
+                                    <field name="start_date" string="Starting at" attrs="{'required': [('allday','=',True)], 'invisible': [('allday','=',False)], 'readonly': [('id', '!=', False), ('recurrency','=',True)]}"/>
+                                    <field name="stop_date" string="Ending at" attrs="{'required': [('allday','=',True)],'invisible': [('allday','=',False)], 'readonly': [('id', '!=', False), ('recurrency','=',True)]}"/>
 
-                                    <field name="start_datetime" string="Starting at" attrs="{'invisible': [('allday','=',True)], 'readonly': [('id', '!=', False), ('recurrency','=',True)]}"/>
+                                    <field name="start_datetime" string="Starting at" attrs="{'required': [('allday','=',False)], 'invisible': [('allday','=',True)], 'readonly': [('id', '!=', False), ('recurrency','=',True)]}"/>
                                     <field name="stop_datetime" invisible="1"/>
                                     <label for="duration" attrs="{'invisible': [('allday','=',True)]}"/>
                                     <div attrs="{'invisible': [('allday','=',True)]}">