--- a/mercurial/help.py	Tue Apr 29 11:40:42 2014 -0700
+++ b/mercurial/help.py	Wed Apr 16 20:01:03 2014 -0400
@@ -481,6 +481,10 @@
                 rst.append('%s:\n\n' % title)
                 rst.extend(minirst.maketable(sorted(matches[t]), 1))
                 rst.append('\n')
+        if not rst:
+            msg = _('no matches')
+            hint = _('try "hg help" for a list of topics')
+            raise util.Abort(msg, hint=hint)
     elif name and name != 'shortlist':
         i = None
         if unknowncmd: