diff -r bc7d465ea11e -r 8a1a51d31e85 mercurial/unionrepo.py
--- a/mercurial/unionrepo.py	Mon May 03 12:21:56 2021 +0200
+++ b/mercurial/unionrepo.py	Mon May 03 12:22:06 2021 +0200
@@ -183,7 +183,7 @@
         filelog.filelog.__init__(self, opener, path)
         filelog2 = filelog.filelog(opener2, path)
         self._revlog = unionrevlog(
-            opener, self.indexfile, filelog2._revlog, linkmapper
+            opener, self._revlog.indexfile, filelog2._revlog, linkmapper
         )
         self._repo = repo
         self.repotiprev = self._revlog.repotiprev