diff -r dd2e25e49862 -r 6eb55310fcbc mercurial/templater.py
--- a/mercurial/templater.py	Fri Mar 07 14:06:52 2014 -0500
+++ b/mercurial/templater.py	Thu Mar 27 17:21:27 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):