Install dm-postgres-adapter on Mac - ruby

Question

I've been fighting on this for two days, time to ask to StackOverflow.
I've prepared a simple Ruby app (noob alert!) to start with this language. I've used Sinatra and DataMapper.
When using MySql everything went fine. I've installed the dm-mysql-adapter and then with a rake migrate the tables where automagically created.
I tried to change mysql over postgres (to publish the app on Heroku) and now the problem.
Launching this command:
sudo gem install dm-postgres-adapter
will give:
Building native extensions. This could take a while...
ERROR: Error installing dm-postgres-adapter:
ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
checking for main() in -lpq... yes
checking for libpq-fe.h... yes
checking for libpq/libpq-fs.h... yes
checking for postgres.h... yes
checking for mb/pg_wchar.h... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
--with-pgsql-server-dir
--without-pgsql-server-dir
--with-pgsql-server-include
--without-pgsql-server-include=${pgsql-server-dir}/include
--with-pgsql-server-lib
--without-pgsql-server-lib=${pgsql-server-dir}/
--with-pgsql-client-dir
--without-pgsql-client-dir
--with-pgsql-client-include
--without-pgsql-client-include=${pgsql-client-dir}/include
--with-pgsql-client-lib
--without-pgsql-client-lib=${pgsql-client-dir}/
--with-pqlib
--without-pqlib
Could not find PostgreSQL build environment (libraries & headers): Makefile not created
I've tried to uninstall and reinstall Postgres (through homebrew) and also passing to the gem install some of those parameters, for example:
sudo gem install dm-postgres-adapter -- --with-pgsql-server-dir=/usr/local/Cellar/postgresql/9.3.2/
sudo gem install dm-postgres-adapter -- --with-pgsql-server-dir=/usr/local/Cellar/postgresql/9.3.2/include/server/
sudo gem install dm-postgres-adapter -- --with-pgsql-server-include=/usr/local/Cellar/postgresql/9.3.2/include/
Any help on this?