--- a/mercurial/patch.py	Sun Oct 06 19:25:18 2019 -0400
+++ b/mercurial/patch.py	Mon Oct 07 00:04:04 2019 -0400
@@ -2626,7 +2626,9 @@
         # filter out copies where source side isn't inside the matcher
         # (copies.pathcopies() already filtered out the destination)
         copy = {
-            dst: src for dst, src in copy.iteritems() if copysourcematch(src)
+            dst: src
+            for dst, src in pycompat.iteritems(copy)
+            if copysourcematch(src)
         }
 
     modifiedset = set(modified)