diff -r 8a6a86c9a5b5 -r 81d6dc8c3c63 mercurial/templater.py
--- a/mercurial/templater.py	Tue Mar 18 14:29:33 2014 -0700
+++ b/mercurial/templater.py	Mon Mar 31 10:12:07 2014 -0500
@@ -212,6 +212,7 @@
             raise error.ParseError(_("filter %s expects one argument") % n)
         f = context._filters[n]
         return (runfilter, (args[0][0], args[0][1], f))
+    raise error.ParseError(_("unknown function '%s'") % n)
 
 def date(context, mapping, args):
     if not (1 <= len(args) <= 2):