Asserting existing key to be primary

I have a table that has a candidate primary key (e.g. - unique, not
null) that I wish to actually assert _is_ a primary key.

Is there a way to do that without too much (mwahahhaha! fiddling with
pg_class!!!) trickery?
--
(format nil "~S(at)~S" "cbbrowne" "acm.org")
http://cbbrowne.com/info/emacs.html
"What we need is either less corruption, or more chance to participate
in it." -- Unknown