diff -r f92f8921a5cc -r e4357c214bf1 mercurial/dispatch.py
--- a/mercurial/dispatch.py	Sat Jul 24 00:38:08 2010 +0200
+++ b/mercurial/dispatch.py	Thu Jul 22 15:26:26 2010 -0400
@@ -248,7 +248,7 @@
         if self.shadows:
             ui.debug("alias '%s' shadows command\n" % self.name)
 
-        return self.fn(ui, *args, **opts)
+        return util.checksignature(self.fn)(ui, *args, **opts)
 
 def addaliases(ui, cmdtable):
     # aliases are processed after extensions have been loaded, so they