diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -14,7 +14,7 @@
 import os
 from i18n import gettext as _
 
-class transaction:
+class transaction(object):
     def __init__(self, report, opener, journal, after=None):
         self.journal = None