diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1395,6 +1395,8 @@ 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
 
diff --git a/tests/test-extension b/tests/test-extension
--- a/tests/test-extension
+++ b/tests/test-extension
@@ -53,3 +53,14 @@ echo '[extensions]' > $HGRCPATH
 echo "barfoo = $barfoopath" >> $HGRCPATH
 cd a
 hg foo
+
+cd ..
+cat > empty.py <<EOF
+'''empty cmdtable
+'''
+cmdtable = {}
+EOF
+emptypath=`pwd`/empty.py
+echo '[extensions]' > $HGRCPATH
+echo "empty = $emptypath" >> $HGRCPATH
+hg help empty
diff --git a/tests/test-extension.out b/tests/test-extension.out
--- a/tests/test-extension.out
+++ b/tests/test-extension.out
@@ -19,3 +19,6 @@ ui.parentui isnot None
 reposetup called for a
 ui == repo.ui
 Foo
+empty extension - empty cmdtable
+
+no commands defined