diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -524,7 +524,7 @@
     if dirtyc1:
         _combinecopies(data2['incomplete'], data1['incomplete'], copy, diverge,
                        incompletediverge)
-    else:
+    if dirtyc2:
         _combinecopies(data1['incomplete'], data2['incomplete'], copy, diverge,
                        incompletediverge)
 
@@ -563,7 +563,13 @@
     for f in bothnew:
         _checkcopies(c1, c2, f, base, tca, dirtyc1, limit, both1)
         _checkcopies(c2, c1, f, base, tca, dirtyc2, limit, both2)
-    if dirtyc1:
+    if dirtyc1 and dirtyc2:
+        remainder = _combinecopies(both2['incomplete'], both1['incomplete'],
+                                   copy, bothdiverge, bothincompletediverge)
+        remainder1 = _combinecopies(both1['incomplete'], both2['incomplete'],
+                                   copy, bothdiverge, bothincompletediverge)
+        remainder.update(remainder1)
+    elif dirtyc1:
         # incomplete copies may only be found on the "dirty" side for bothnew
         assert not both2['incomplete']
         remainder = _combinecopies({}, both1['incomplete'], copy, bothdiverge,
diff --git a/tests/test-copytrace-heuristics.t b/tests/test-copytrace-heuristics.t
--- a/tests/test-copytrace-heuristics.t
+++ b/tests/test-copytrace-heuristics.t
@@ -930,51 +930,28 @@
 
   $ hg graft -r 6 --base c9241b0f2d5b --hidden
   grafting 6:99802e4f1e46 "added willconflict and d" (tip)
-  ** unknown exception encountered, please report by visiting
-  ** https://mercurial-scm.org/wiki/BugTracker
-  ** Python 2.7.12 (default, Nov 12 2018, 14:36:49) [GCC 5.4.0 20160609]
-  ** Mercurial Distributed SCM (version 4.8.1+539-b6c610bf567e+20181221)
-  ** Extensions loaded: rebase, shelve
-  Traceback (most recent call last):
-    File "/home/khanchi/hg/hg-committed/hg", line 43, in <module>
-      dispatch.run()
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 99, in run
-      status = dispatch(req)
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 225, in dispatch
-      ret = _runcatch(req) or 0
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 376, in _runcatch
-      return _callcatch(ui, _runcatchfunc)
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 384, in _callcatch
-      return scmutil.callcatch(ui, func)
-    File "/home/khanchi/hg/hg-committed/mercurial/scmutil.py", line 165, in callcatch
-      return func()
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 367, in _runcatchfunc
-      return _dispatch(req)
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 1021, in _dispatch
-      cmdpats, cmdoptions)
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 756, in runcommand
-      ret = _runcommand(ui, options, cmd, d)
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 1030, in _runcommand
-      return cmdfunc()
-    File "/home/khanchi/hg/hg-committed/mercurial/dispatch.py", line 1018, in <lambda>
-      d = lambda: util.checksignature(func)(ui, *args, **strcmdopt)
-    File "/home/khanchi/hg/hg-committed/mercurial/util.py", line 1676, in check
-      return func(*args, **kwargs)
-    File "/home/khanchi/hg/hg-committed/mercurial/commands.py", line 2378, in graft
-      return _dograft(ui, repo, *revs, **opts)
-    File "/home/khanchi/hg/hg-committed/mercurial/commands.py", line 2590, in _dograft
-      stats = mergemod.graft(repo, ctx, base, ['local', 'graft'])
-    File "/home/khanchi/hg/hg-committed/mercurial/merge.py", line 2234, in graft
-      mergeancestor=mergeancestor, labels=labels)
-    File "/home/khanchi/hg/hg-committed/mercurial/merge.py", line 2075, in update
-      followcopies, matcher=matcher, mergeforce=mergeforce)
-    File "/home/khanchi/hg/hg-committed/mercurial/merge.py", line 1342, in calculateupdates
-      acceptremote, followcopies)
-    File "/home/khanchi/hg/hg-committed/mercurial/merge.py", line 1146, in manifestmerge
-      ret = copies.mergecopies(repo, wctx, p2, pa)
-    File "/home/khanchi/hg/hg-committed/mercurial/copies.py", line 416, in mergecopies
-      return _fullcopytracing(repo, c1, c2, base)
-    File "/home/khanchi/hg/hg-committed/mercurial/copies.py", line 568, in _fullcopytracing
-      assert not both2['incomplete']
-  AssertionError
-  [1]
+  merging willconflict
+  warning: conflicts while merging willconflict! (edit, then use 'hg resolve --mark')
+  abort: unresolved conflicts, can't continue
+  (use 'hg resolve' and 'hg graft --continue')
+  [255]
+
+  $ hg diff
+  diff -r 9a8bb7cc6814 willconflict
+  --- a/willconflict	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/willconflict	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,1 +1,5 @@
+  +<<<<<<< local: 9a8bb7cc6814 - test: added c
+   foobar
+  +=======
+  +barfoo
+  +>>>>>>> graft: 99802e4f1e46 - test: added willconflict and d
+
+  $ echo barfoo > willconflict
+  $ hg resolve -m
+  (no more unresolved files)
+  continue: hg graft --continue
+  $ hg graft --continue
+  grafting 6:99802e4f1e46 "added willconflict and d" (tip)
+  $ cd ..
+  $ rm -rf repo