diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -481,6 +481,10 @@ def help_(ui, name, unknowncmd=False, fu
                 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:
diff --git a/tests/test-help.t b/tests/test-help.t
--- a/tests/test-help.t
+++ b/tests/test-help.t
@@ -988,6 +988,13 @@ Test keyword search help
   
    qclone clone main and patch repository at same time
 
+Test unfound keyword
+
+  $ hg help --keyword nonexistingwordthatwillneverexisteverever
+  abort: no matches
+  (try "hg help" for a list of topics)
+  [255]
+
 Test omit indicating for help
 
   $ cat > addverboseitems.py <<EOF