--- a/mercurial/templater.py	Thu Sep 24 01:06:10 2015 -0700
+++ b/mercurial/templater.py	Thu Sep 24 01:06:41 2015 -0700
@@ -833,7 +833,7 @@
 
 class templater(object):
 
-    def __init__(self, mapfile, filters=None, defaults={}, cache={},
+    def __init__(self, mapfile, filters=None, defaults=None, cache={},
                  minchunk=1024, maxchunk=65536):
         '''set up template engine.
         mapfile is name of file to read map definitions from.
@@ -841,6 +841,8 @@
         defaults is dict of default map definitions.'''
         if filters is None:
             filters = {}
+        if defaults is None:
+            defaults = {}
         self.mapfile = mapfile or 'template'
         self.cache = cache.copy()
         self.map = {}