--- a/mercurial/mail.py	Sun Oct 06 13:17:19 2019 -0400
+++ b/mercurial/mail.py	Sun Oct 06 13:28:56 2019 -0400
@@ -19,6 +19,7 @@
 import time
 
 from .i18n import _
+from .pycompat import open
 from . import (
     encoding,
     error,