diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -453,7 +453,7 @@
 addtopichook('config', inserttweakrc)
 
 def help_(ui, commands, name, unknowncmd=False, full=True, subtopic=None,
-          **opts):
+          fullname=None, **opts):
     '''
     Generate the help for 'name' as unformatted restructured text. If
     'name' is None, describe the commands available.
@@ -816,8 +816,16 @@
             if unknowncmd:
                 raise error.UnknownCommand(name)
             else:
-                msg = _('no such help topic: %s') % name
-                hint = _("try 'hg help --keyword %s'") % name
+                if fullname:
+                    formatname = fullname
+                else:
+                    formatname = name
+                if subtopic:
+                    hintname = subtopic
+                else:
+                    hintname = name
+                msg = _('no such help topic: %s') % formatname
+                hint = _("try 'hg help --keyword %s'") % hintname
                 raise error.Abort(msg, hint=hint)
     else:
         # program name
@@ -852,7 +860,7 @@
     termwidth = ui.termwidth() - 2
     if textwidth <= 0 or termwidth < textwidth:
         textwidth = termwidth
-    text = help_(ui, commands, name,
+    text = help_(ui, commands, name, fullname=fullname,
                  subtopic=subtopic, unknowncmd=unknowncmd, full=full, **opts)
 
     blocks, pruned = minirst.parse(text, keep=keep)
diff --git a/tests/test-help.t b/tests/test-help.t
--- a/tests/test-help.t
+++ b/tests/test-help.t
@@ -1303,6 +1303,13 @@
       *empty chunk* at the end of each *delta group* denotes the boundary to the
       next filelog sub-segment.
 
+non-existent subtopics print an error
+
+  $ hg help internals.foo
+  abort: no such help topic: internals.foo
+  (try 'hg help --keyword foo')
+  [255]
+
 test advanced, deprecated and experimental options are hidden in command help
   $ hg help debugoptADV
   hg debugoptADV