--- a/mercurial/copies.py	Mon Oct 03 16:19:55 2016 +0200
+++ b/mercurial/copies.py	Mon Oct 03 13:18:31 2016 +0200
@@ -331,7 +331,8 @@
     m2 = c2.manifest()
     ma = ca.manifest()
 
-    copy1, copy2, = {}, {}
+    # see checkcopies documentation below for these dicts
+    copy1, copy2 = {}, {}
     movewithdir1, movewithdir2 = {}, {}
     fullcopy1, fullcopy2 = {}, {}
     diverge = {}