--- a/mercurial/ui.py	Mon Jun 26 17:20:46 2017 +0530
+++ b/mercurial/ui.py	Sun Jun 25 03:11:55 2017 +0530
@@ -1257,7 +1257,7 @@
         # prompt to start parsing. Sadly, we also can't rely on
         # choices containing spaces, ASCII, or basically anything
         # except an ampersand followed by a character.
-        m = re.match(r'(?s)(.+?)\$\$([^\$]*&[^ \$].*)', prompt)
+        m = re.match(br'(?s)(.+?)\$\$([^\$]*&[^ \$].*)', prompt)
         msg = m.group(1)
         choices = [p.strip(' ') for p in m.group(2).split('$$')]
         return (msg,