--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1340,7 +1340,7 @@ def help_(ui, name=None, with_version=Fa
 
             addglobalopts(False)
 
-    def helplist(select=None):
+    def helplist(header, select=None):
         h = {}
         cmds = {}
         for c, e in table.items():
@@ -1358,6 +1358,11 @@ def help_(ui, name=None, with_version=Fa
             h[f] = doc.splitlines(0)[0].rstrip()
             cmds[f] = c.lstrip("^")
 
+        if not h:
+            ui.status(_('no commands defined\n'))
+            return
+
+        ui.status(header)
         fns = h.keys()
         fns.sort()
         m = max(map(len, fns))
@@ -1407,14 +1412,10 @@ def help_(ui, name=None, with_version=Fa
         try:
             ct = mod.cmdtable
         except AttributeError:
-            ct = None
-        if not ct:
-            ui.status(_('no commands defined\n'))
-            return
-
-        ui.status(_('list of commands:\n\n'))
+            ct = {}
+
         modcmds = dict.fromkeys([c.split('|', 1)[0] for c in ct])
-        helplist(modcmds.has_key)
+        helplist(_('list of commands:\n\n'), modcmds.has_key)
 
     if name and name != 'shortlist':
         i = None
@@ -1438,11 +1439,11 @@ def help_(ui, name=None, with_version=Fa
 
         # list of commands
         if name == "shortlist":
-            ui.status(_('basic commands:\n\n'))
+            header = _('basic commands:\n\n')
         else:
-            ui.status(_('list of commands:\n\n'))
-
-        helplist()
+            header = _('list of commands:\n\n')
+
+        helplist(header)
 
     # list all option lists
     opt_output = []

--- a/tests/test-extension
+++ b/tests/test-extension
@@ -64,3 +64,18 @@ emptypath=`pwd`/empty.py
 echo '[extensions]' > $HGRCPATH
 echo "empty = $emptypath" >> $HGRCPATH
 hg help empty
+
+cat > debugextension.py <<EOF
+'''only debugcommands
+'''
+def debugfoobar(ui, repo, *args, **opts):
+    "yet another debug command"
+    pass
+
+cmdtable = {"debugfoobar": (debugfoobar, (), "hg debugfoobar")}
+EOF
+debugpath=`pwd`/debugextension.py
+echo '[extensions]' > $HGRCPATH
+echo "debugextension = $debugpath" >> $HGRCPATH
+hg help debugextension
+hg --debug help debugextension

--- a/tests/test-extension.out
+++ b/tests/test-extension.out
@@ -22,3 +22,30 @@ Foo
 empty extension - empty cmdtable
 
 no commands defined
+debugextension extension - only debugcommands
+
+no commands defined
+debugextension extension - only debugcommands
+
+list of commands:
+
+ debugfoobar:
+      yet another debug command
+
+global options:
+ -R --repository      repository root directory or symbolic path name
+    --cwd             change working directory
+ -y --noninteractive  do not prompt, assume 'yes' for any required answers
+ -q --quiet           suppress output
+ -v --verbose         enable additional output
+    --config          set/override config option
+    --debug           enable debugging output
+    --debugger        start debugger
+    --encoding        set the charset encoding (default: ascii)
+    --encodingmode    set the charset encoding mode (default: strict)
+    --lsprof          print improved command execution profile
+    --traceback       print traceback on exception
+    --time            time how long the command takes
+    --profile         print command execution profile
+    --version         output version information and exit
+ -h --help            display help and exit