diff --git a/offlineimap/mbnames.py b/offlineimap/mbnames.py
index a972358..57b95a1 100644
--- a/offlineimap/mbnames.py
+++ b/offlineimap/mbnames.py
@@ -120,7 +120,7 @@ class _IntermediateMbnames():
                 json.dump(itemlist, intermediateFD)
 
 
-class _Mbnames():
+class _Mbnames:
     def __init__(self, config, ui, dry_run):
 
         self._config = config