diff --git a/ietf/meeting/models.py b/ietf/meeting/models.py
index e7ebbe324..382f6dc27 100644
--- a/ietf/meeting/models.py
+++ b/ietf/meeting/models.py
@@ -793,7 +793,7 @@ class SchedTimeSessAssignment(models.Model):
         if not self.timeslot:
             components.append("unknown")
 
-        if not self.session or not (getattr(self.session, "historic_group") or self.session.group):
+        if not self.session or not (getattr(self.session, "historic_group", None) or self.session.group):
             components.append("unknown")
         else:
             components.append(self.timeslot.time.strftime("%Y-%m-%d-%a-%H%M"))