diff --git a/patoolib/baker.py b/patoolib/baker.py
index bd8a204..058a7f0 100644
--- a/patoolib/baker.py
+++ b/patoolib/baker.py
@@ -478,7 +478,7 @@ class Baker(object):
             # use that.
             cmd = self.defaultcommand
             if cmd is None:
-                raise CommandError("No command specified")
+                raise CommandError("unknown command `%s' specified" % argv[1])
 
             options = argv[1:]