diff --git a/offlineimap/folder/Maildir.py b/offlineimap/folder/Maildir.py
index 9df641c..6e388fc 100644
--- a/offlineimap/folder/Maildir.py
+++ b/offlineimap/folder/Maildir.py
@@ -466,7 +466,7 @@ class MaildirFolder(BaseFolder):
                         an efficient rename.
         """
 
-        if not uid in self.messagelist:
+        if uid not in self.messagelist:
             raise OfflineImapError("Cannot change unknown Maildir UID %s" % uid,
                                    OfflineImapError.ERROR.MESSAGE)
         if uid == new_uid: return