diff -r 4dacd0cef146 -r d37975386798 mercurial/chgserver.py
--- a/mercurial/chgserver.py	Thu Mar 26 10:09:17 2020 -0400
+++ b/mercurial/chgserver.py	Tue Mar 31 15:11:33 2020 +0530
@@ -528,7 +528,7 @@
     def _setumask(self, data):
         mask = struct.unpack(b'>I', data)[0]
         self.ui.log(b'chgserver', b'setumask %r\n', mask)
-        os.umask(mask)
+        util.setumask(mask)
 
     def runcommand(self):
         # pager may be attached within the runcommand session, which should