diff --git a/ietf/meeting/forms.py b/ietf/meeting/forms.py
index d20275259..5099c7dcf 100644
--- a/ietf/meeting/forms.py
+++ b/ietf/meeting/forms.py
@@ -84,7 +84,7 @@ class InterimSessionInlineFormSet(BaseInlineFormSet):
             dates.sort()
             last_date = dates[0]
             for date in dates[1:]:
-                if last_date.day + 1 != date.day:
+                if date - last_date != datetime.timedelta(days=1):
                     raise forms.ValidationError('For Multi-Day meetings, days must be consecutive')
                 last_date = date