Error when installing Postgres gem

terminal

  ✘ Sulcalibur@Ultra-Magnus  ~/Sites/crumblr   master ●  sudo gem install pg
 Building native extensions.  This could take a while...
 ERROR:  Error installing pg:
 	ERROR: Failed to build gem native extension.
 
 		/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r ./siteconf20150501-20896-bbd4c6.rb extconf.rb
 checking for pg_config... yes
 Using config values from /usr/local/bin/pg_config
 checking for libpq-fe.h... yes
 checking for libpq/libpq-fs.h... yes
 checking for pg_config_manual.h... yes
 checking for PQconnectdb() in -lpq... no
 checking for PQconnectdb() in -llibpq... no
 checking for PQconnectdb() in -lms/libpq... no
 Can't find the PostgreSQL client library (libpq)
 *** 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-pg
 	--without-pg
 	--enable-windows-cross
 	--disable-windows-cross
 	--with-pg-config
 	--without-pg-config
 	--with-pg_config
 	--without-pg_config
 	--with-pg-dir
 	--without-pg-dir
 	--with-pg-include
 	--without-pg-include=${pg-dir}/include
 	--with-pg-lib
 	--without-pg-lib=${pg-dir}/
 	--with-pqlib
 	--without-pqlib
 	--with-libpqlib
 	--without-libpqlib
 	--with-ms/libpqlib
 	--without-ms/libpqlib
 
 extconf failed, exit code 1
 
 Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/pg-0.18.1 for inspection.
 Results logged to /Library/Ruby/Gems/2.0.0/extensions/universal-darwin-14/2.0.0/pg-0.18.1/gem_make.out
  ✘ Sulcalibur@Ultra-Magnus  ~/Sites/crumblr   master ● gm