diff --git a/doc/runrst b/doc/runrst
--- a/doc/runrst
+++ b/doc/runrst
@@ -27,8 +27,7 @@
                      "http://docutils.sourceforge.net/\n")
     sys.exit(-1)
 
-def role_hg(name, rawtext, text, lineno, inliner,
-            options={}, content=[]):
+def role_hg(name, rawtext, text, lineno, inliner, options=None, content=None):
     text = "hg " + utils.unescape(text)
     linktext = nodes.literal(rawtext, text)
     parts = text.split()