diff -r 5698c5eee12b -r 1bd33932713d mercurial/bundlerepo.py
--- a/mercurial/bundlerepo.py	Thu Apr 29 22:01:04 2021 +0200
+++ b/mercurial/bundlerepo.py	Tue Jan 31 11:41:59 2023 +0100
@@ -533,6 +533,8 @@
     try:
         repo = localrepo.instance(ui, repopath, create=False)
         tempparent = None
+    except error.RequirementError:
+        raise  # no fallback if the backing repo is unsupported
     except error.RepoError:
         tempparent = pycompat.mkdtemp()
         try: