diff -r 08c6d6962b2a -r 2c10876bb320 mercurial/merge.py
--- a/mercurial/merge.py	Wed Sep 16 10:09:37 2020 -0700
+++ b/mercurial/merge.py	Thu Sep 17 09:23:21 2020 -0700
@@ -1398,9 +1398,8 @@
     _prefetchfiles(repo, mctx, mresult)
 
     updated, merged, removed = 0, 0, 0
-    ms = mergestatemod.mergestate.clean(
-        repo, wctx.p1().node(), mctx.node(), labels
-    )
+    ms = mergestatemod.mergestate.clean(repo)
+    ms.start(wctx.p1().node(), mctx.node(), labels)
 
     for f, op in pycompat.iteritems(mresult.commitinfo):
         # the other side of filenode was choosen while merging, store this in