diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -458,12 +458,14 @@
         create = allowcreate and not r.wvfs.exists(b'%s/.hg' % path)
         # repository constructor does expand variables in path, which is
         # unsafe since subrepo path might come from untrusted source.
-        if os.path.realpath(util.expandpath(root)) != root:
+        norm_root = os.path.normcase(root)
+        real_root = os.path.normcase(os.path.realpath(util.expandpath(root)))
+        if real_root != norm_root:
             raise error.Abort(
                 _(b'subrepo path contains illegal component: %s') % path
             )
         self._repo = hg.repository(r.baseui, root, create=create)
-        if self._repo.root != root:
+        if os.path.normcase(self._repo.root) != os.path.normcase(root):
             raise error.ProgrammingError(
                 b'failed to reject unsafe subrepo '
                 b'path: %s (expanded to %s)' % (root, self._repo.root)