--- a/hgext/mq.py	Thu Sep 24 00:49:02 2015 -0700
+++ b/hgext/mq.py	Thu Sep 24 00:50:06 2015 -0700
@@ -483,7 +483,7 @@
         self.guardsdirty = False
         self.activeguards = None
 
-    def diffopts(self, opts={}, patchfn=None):
+    def diffopts(self, opts=None, patchfn=None):
         diffopts = patchmod.diffopts(self.ui, opts)
         if self.gitmode == 'auto':
             diffopts.upgrade = True