diff --git a/openslides/agenda/views.py b/openslides/agenda/views.py
index d2da48159..42356906a 100644
--- a/openslides/agenda/views.py
+++ b/openslides/agenda/views.py
@@ -58,7 +58,8 @@ class Overview(TemplateView):
         duration = timedelta()
 
         for item in items:
-            if not item.closed and len(item.duration) > 0:
+            if not item.closed and (item.duration is not None
+                                    and len(item.duration) > 0):
                 duration_list = item.duration.split(':')
                 duration += timedelta(hours=int(duration_list[0]),
                                       minutes=int(duration_list[1]))