diff --git a/mercurial/copies.py b/mercurial/copies.py
--- a/mercurial/copies.py
+++ b/mercurial/copies.py
@@ -532,7 +532,10 @@
     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:
+        pass
+    elif dirtyc1:
         # incomplete copies may only be found on the "dirty" side for bothnew
         assert not both2['incomplete']
         remainder = _combinecopies({}, both1['incomplete'], copy, bothdiverge,