--- a/hgext/chgserver.py	Thu Oct 20 23:40:24 2016 +0900
+++ b/hgext/chgserver.py	Thu Oct 20 23:53:36 2016 +0900
@@ -232,7 +232,7 @@
             # these situations and will behave differently (write to stdout).
             if (any(s[1] for s in self._bufferstates)
                 or not util.safehasattr(self.fout, 'fileno')
-                or self.fout.fileno() != sys.stdout.fileno()):
+                or self.fout.fileno() != util.stdout.fileno()):
                 return super(chgui, self).system(cmd, environ, cwd, onerr,
                                                  errprefix)
             # copied from mercurial/util.py:system()