--- a/mercurial/mail.py	Thu Oct 24 16:34:43 2019 +0200
+++ b/mercurial/mail.py	Thu Oct 24 14:28:20 2019 +0200
@@ -342,6 +342,7 @@
         s.decode('ascii')
     except UnicodeDecodeError:
         for ics in (encoding.encoding, encoding.fallbackencoding):
+            ics = pycompat.sysstr(ics)
             try:
                 u = s.decode(ics)
             except UnicodeDecodeError: