diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2034,7 +2034,7 @@ def help_(ui, name=None, with_version=Fa
                        'extensions\n'))
 
     def helpextcmd(name):
-        cmd, ext, mod = extensions.disabledcmd(name, ui.config('ui', 'strict'))
+        cmd, ext, mod = extensions.disabledcmd(ui, name, ui.config('ui', 'strict'))
         doc = gettext(mod.__doc__).splitlines()[0]
 
         msg = help.listexts(_("'%s' is provided by the following "
diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -248,7 +248,7 @@ def disabledext(name):
     if name in paths:
         return _disabledhelp(paths[name])
 
-def disabledcmd(cmd, strict=False):
+def disabledcmd(ui, cmd, strict=False):
     '''import disabled extensions until cmd is found.
     returns (cmdname, extname, doc)'''
 
@@ -266,6 +266,10 @@ def disabledcmd(cmd, strict=False):
                 getattr(mod, 'cmdtable', {}), strict)
         except (error.AmbiguousCommand, error.UnknownCommand):
             return
+        except Exception:
+            ui.warn(_('warning: error finding commands in %s\n') % path)
+            ui.traceback()
+            return
         for c in aliases:
             if c.startswith(cmd):
                 cmd = c
diff --git a/tests/test-extension.t b/tests/test-extension.t
--- a/tests/test-extension.t
+++ b/tests/test-extension.t
@@ -315,6 +315,11 @@ Broken disabled extension and command:
   
   use "hg help extensions" for information on enabling extensions
 
+  $ cat > hgext/forest.py <<EOF
+  > cmdtable = None
+  > EOF
   $ hg --config extensions.path=./path.py help foo > /dev/null
+  warning: error finding commands in $TESTTMP/hgext/forest.py
   hg: unknown command 'foo'
+  warning: error finding commands in $TESTTMP/hgext/forest.py
   [255]