diff -r 9d0d8793e847 -r 91701785c2c5 mercurial/subrepo.py
--- a/mercurial/subrepo.py	Mon Feb 11 15:41:08 2019 +0300
+++ b/mercurial/subrepo.py	Mon Feb 11 11:18:37 2019 -0500
@@ -404,7 +404,7 @@
         super(hgsubrepo, self).__init__(ctx, path)
         self._state = state
         r = ctx.repo()
-        root = r.wjoin(path)
+        root = r.wjoin(util.localpath(path))
         create = allowcreate and not r.wvfs.exists('%s/.hg' % path)
         # repository constructor does expand variables in path, which is
         # unsafe since subrepo path might come from untrusted source.