diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -236,10 +236,12 @@ def help_(ui, name, unknowncmd=False, fu
 
         # check if it's an invalid alias and display its error if it is
         if getattr(entry[0], 'badalias', None):
-            if not unknowncmd:
-                ui.pushbuffer()
-                entry[0](ui)
-                rst.append(ui.popbuffer())
+            rst.append(entry[0].badalias + '\n')
+            if entry[0].unknowncmd:
+                try:
+                    rst.extend(helpextcmd(entry[0].cmdname))
+                except error.UnknownCommand:
+                    pass
             return rst
 
         # synopsis
diff --git a/tests/test-alias.t b/tests/test-alias.t
--- a/tests/test-alias.t
+++ b/tests/test-alias.t
@@ -98,6 +98,7 @@ disabled
   [255]
   $ hg help disabled
   alias 'disabled' resolves to unknown command 'email'
+  
   'email' is provided by the following extension:
   
       patchbomb     command to send changesets as (a series of) patch emails
@@ -129,7 +130,8 @@ invalid options
   error in definition for alias 'no--cwd': --cwd may only be given on the command line
   [255]
   $ hg help no--cwd
-  error in definition for alias 'no--cwd': --cwd may only be given on the command line
+  error in definition for alias 'no--cwd': --cwd may only be given on the
+  command line
   $ hg no-R
   error in definition for alias 'no-R': -R may only be given on the command line
   [255]
@@ -139,12 +141,14 @@ invalid options
   error in definition for alias 'no--repo': --repo may only be given on the command line
   [255]
   $ hg help no--repo
-  error in definition for alias 'no--repo': --repo may only be given on the command line
+  error in definition for alias 'no--repo': --repo may only be given on the
+  command line
   $ hg no--repository
   error in definition for alias 'no--repository': --repository may only be given on the command line
   [255]
   $ hg help no--repository
-  error in definition for alias 'no--repository': --repository may only be given on the command line
+  error in definition for alias 'no--repository': --repository may only be given
+  on the command line
   $ hg no--config
   error in definition for alias 'no--config': --config may only be given on the command line
   [255]