diff -r 5a59a0ed0a37 -r 0afe96e374a7 mercurial/subrepo.py
--- a/mercurial/subrepo.py	Thu Apr 15 09:23:19 2021 +0200
+++ b/mercurial/subrepo.py	Thu Apr 15 09:23:28 2021 +0200
@@ -873,7 +873,8 @@
             opts = copy.copy(opts)
             opts.pop(b'rev', None)
             opts.pop(b'branch', None)
-        return hg.outgoing(ui, self._repo, _abssource(self._repo, True), opts)
+        subpath = subrepoutil.repo_rel_or_abs_source(self._repo)
+        return hg.outgoing(ui, self._repo, dest, opts, subpath=subpath)
 
     @annotatesubrepoerror
     def incoming(self, ui, source, opts):