diff -r 959ebff3505a -r 5a909a8098a1 mercurial/copies.py
--- a/mercurial/copies.py	Tue Mar 07 09:56:11 2017 -0800
+++ b/mercurial/copies.py	Tue Mar 07 09:56:11 2017 -0800
@@ -149,10 +149,7 @@
     """
     ma = a.manifest()
     mb = b.manifest()
-    if match:
-        ma = ma.matches(match)
-        mb = mb.matches(match)
-    return mb.filesnotin(ma)
+    return mb.filesnotin(ma, match=match)
 
 def _forwardcopies(a, b, match=None):
     '''find {dst@b: src@a} copy mapping where a is an ancestor of b'''