Superuser accout (PostgreSQL 9.0.4)

Hi,

I have standard main 5432 cluster with postgres owner/superuser. I made:

su -c "su - postgres"
psql -c "\du"
List of roles
Role name | Attributes | Member of
-----------+-----------------------------------+-----------
postgres | Superuser, Create role, Create DB | {}

psql -c "ALTER ROLE postgres NOSUPERUSER"

After this there is no superuser in cluster 9.0/main, and I can't
restore it to previous point:

psql -c "ALTER ROLE postgres SUPERUSER"
ERROR: must be superuser to alter superusers

createuser -srd admin
createuser: creation of new role failed: ERROR: must be superuser to
create superusers

psql -c "UPDATE pg_authid SET rolsuper = true WHERE rolname = 'postgres'"

(rolcatupdate change to false, so obviously above doesn't work)

Is there any way to restore superuser without recreating cluster from
scratch (initdb, pg_createcluster etc.) ? Or better should PostgreSQL
prevent for such situation (mistake command) ? I don't know is there
any "at least one superuser per cluster rule" (?)

Thanks,
Grzegorz Sz.