mac os 10.6, ports, postgresql, rvm and the pg gem

i hope i hit all the necessary keywords with the title so you can find this one on google.
because if you, just like me, are switching to rvm on your mac os development environment and installed your postgresql via ports
gem install pg
will fail telling you, that you are missing the right headers.
gem install pg -- --with-opt-include=/opt/local/include/postgresql84/
--with-opt-lib=/opt/local/lib/postgresql84/
will fix that for you.