diff --git a/kallithea/model/comment.py b/kallithea/model/comment.py
--- a/kallithea/model/comment.py
+++ b/kallithea/model/comment.py
@@ -28,7 +28,7 @@ Original author and date, and relevant c
 import logging
 
 from pylons.i18n.translation import _
-from sqlalchemy.util.compat import defaultdict
+from collections import defaultdict
 
 from kallithea.lib.utils2 import extract_mentioned_users, safe_unicode
 from kallithea.lib import helpers as h