--- a/mercurial/posix.py	Wed Jan 30 03:50:31 2019 +0530
+++ b/mercurial/posix.py	Sat Feb 02 04:49:42 2019 +0530
@@ -583,6 +583,7 @@
     """Return the list of members of the group with the given
     name, KeyError if the group does not exist.
     """
+    name = pycompat.sysstr(name)
     return list(grp.getgrnam(name).gr_mem)
 
 def spawndetached(args):