Use pickle serializer

misago/settings_base.py

@@ -236,6 +236,9 @@ CACHES = {
     }
 }
 
+# Use oldchool serializer
+SESSION_SERIALIZER = 'django.contrib.sessions.serializers.PickleSerializer'
+
 # A sample logging configuration. The only tangible logging
 # performed by this configuration is to send an email to
 # the site admins on every HTTP 500 error when DEBUG=False.