diff -r 3800a6aafb6f -r 279df499511e mercurial/subrepo.py
--- a/mercurial/subrepo.py	Wed Apr 14 17:29:27 2021 +0200
+++ b/mercurial/subrepo.py	Wed Apr 14 17:41:02 2021 +0200
@@ -882,7 +882,8 @@
             opts = copy.copy(opts)
             opts.pop(b'rev', None)
             opts.pop(b'branch', None)
-        return hg.incoming(ui, self._repo, _abssource(self._repo, False), opts)
+        subpath = subrepoutil.repo_rel_or_abs_source(self._repo)
+        return hg.incoming(ui, self._repo, source, opts, subpath=subpath)
 
     @annotatesubrepoerror
     def files(self):