diff --git a/tabellio/agenda/event.py b/tabellio/agenda/event.py
index e801a14..6e6b475 100644
--- a/tabellio/agenda/event.py
+++ b/tabellio/agenda/event.py
@@ -24,7 +24,7 @@ class IBaseEvent(form.Schema):
     place = schema.TextLine(title=_(u'Place'))
 
     start = schema.Datetime(title=_(u'Start'))
-    end = schema.Datetime(title=_(u'End'))
+    end = schema.Datetime(title=_(u'End'), required=False)