diff -r b479fc425a81 -r c2effd1ecebf mercurial/encoding.py
--- a/mercurial/encoding.py	Sat Dec 12 22:57:48 2015 -0500
+++ b/mercurial/encoding.py	Sat Dec 12 23:26:12 2015 -0800
@@ -407,7 +407,7 @@
 
     if not _jsonmap:
         for x in xrange(32):
-            _jsonmap[chr(x)] = "\u%04x" %x
+            _jsonmap[chr(x)] = "\\u%04x" % x
         for x in xrange(32, 256):
             c = chr(x)
             _jsonmap[c] = c