diff -r c0a6c19690ff -r 75979c8d4572 mercurial/ui.py
--- a/mercurial/ui.py	Thu Oct 12 19:20:04 2017 -0700
+++ b/mercurial/ui.py	Thu Oct 12 23:30:46 2017 -0700
@@ -1041,7 +1041,7 @@
         # gracefully and tell the user about their broken pager.
         shell = any(c in command for c in "|&;<>()$`\\\"' \t\n*?[#~=%")
 
-        if pycompat.osname == 'nt' and not shell:
+        if pycompat.iswindows and not shell:
             # Window's built-in `more` cannot be invoked with shell=False, but
             # its `more.com` can.  Hide this implementation detail from the
             # user so we can also get sane bad PAGER behavior.  MSYS has