--- a/mercurial/merge.py	Fri Dec 27 13:03:40 2019 -0800
+++ b/mercurial/merge.py	Mon Jan 06 15:24:36 2020 -0800
@@ -2635,7 +2635,7 @@
         repo.setparents(pctx.node(), pother)
         repo.dirstate.write(repo.currenttransaction())
         # fix up dirstate for copies and renames
-        copies.duplicatecopies(repo, wctx, ctx.rev(), base.rev())
+        copies.graftcopies(repo, wctx, ctx, base)
     return stats