diff --git a/src/mahjong_ranking/models.py b/src/mahjong_ranking/models.py
index 6a7d589..c1f3afe 100644
--- a/src/mahjong_ranking/models.py
+++ b/src/mahjong_ranking/models.py
@@ -626,9 +626,9 @@ def update_ranking(sender, instance, **kwargs):
             instance.player4):
         LOGGER.debug(
             "marking %(user)s's kyu/dan for recalculation since %(start)s",
-            {'user': user, 'start': str(instance.start.date())}
+            {'user': user, 'start': str(instance.start)}
         )
-        set_dirty(user=user.id, hanchan_date=instance.start.date())
+        set_dirty(user=user.id, hanchan_date=instance.start)
         LOGGER.debug("marking event %s for recalculation.", instance.event)
         set_dirty(event=instance.event_id, user=user.id)
         if instance.season: