How to extend subkey's expiry date?

[Adam Funk]

My key expired recently and GPG would (of course) not let me encrypt
to it.  I'd like to keep using the same key.  So I used "gpg
--edit-key" and the "expire" subcommand to extend the expiry date.
Unfortunately the only subkey's expiry date did not change, so I still
can't encrypt to the key.

$ gpg --edit-key e3c5ee5e
...
pub  1024D/E3C5EE5E  created: 2002-02-19  expires: 2007-03-07  usage: CS  
                     trust: ultimate      validity: ultimate
sub  2048g/66796190  created: 2002-02-19  expired: 2005-02-18  usage: E   
...

I've tried using "expire sub" and "expire 66796190" commands inside
edit-key, but I can't change the expiry of the subkey.

Is it possible to do so, or do I need to add a new subkey to keep
using the same main key?

-- 
Thanks,
Adam