diff -r 8a1a51d31e85 -r a07d5cb03a85 mercurial/changegroup.py
--- a/mercurial/changegroup.py	Mon May 03 12:22:06 2021 +0200
+++ b/mercurial/changegroup.py	Mon May 03 12:22:16 2021 +0200
@@ -804,10 +804,10 @@
                 # We failed to resolve a parent for this node, so
                 # we crash the changegroup construction.
                 if util.safehasattr(store, 'target'):
-                    target = store.indexfile
+                    target = store._indexfile
                 else:
                     # some revlog not actually a revlog
-                    target = store._revlog.indexfile
+                    target = store._revlog._indexfile
 
                 raise error.Abort(
                     b"unable to resolve parent while packing '%s' %r"