diff -r 873eb5db89c8 -r 942a5a34b2d0 mercurial/cmdutil.py
--- a/mercurial/cmdutil.py	Tue Feb 03 21:56:29 2015 +0900
+++ b/mercurial/cmdutil.py	Mon Feb 02 14:26:47 2015 -0500
@@ -1091,8 +1091,8 @@
 
             if copies:
                 self.ui.write(',\n  "copies": {%s}' %
-                              ", ".join('"%s": %s' % (j(k), j(copies[k]))
-                                                      for k in copies))
+                              ", ".join('"%s": "%s"' % (j(k), j(v))
+                                                        for k, v in copies))
 
         matchfn = self.matchfn
         if matchfn: