diff --git a/addons/base_calendar/base_calendar_view.xml b/addons/base_calendar/base_calendar_view.xml
index d6430ca98a2..bcc30fe0a81 100644
--- a/addons/base_calendar/base_calendar_view.xml
+++ b/addons/base_calendar/base_calendar_view.xml
@@ -82,7 +82,7 @@
                                 <field name="event_date" />
                                 <field name="event_end_date" />
                                 <field name="language"/>
-                                <field name="ref" colspan="4"/>
+                                <field name="ref" colspan="4" readonly="1"/>
                             </group>
             			</page>
             			<page string="Delegation Info">