sensu-chef: gem 'pg' could not be installed

/opt/sensu/embedded/bin/gem install pg -q --no-rdoc --no-ri
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
        ERROR: Failed to build gem native extension.

    /opt/sensu/embedded/bin/ruby extconf.rb
checking for pg_config... yes
Using config values from /usr/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
        --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=/opt/sensu/embedded/bin/ruby
        --with-pg
        --without-pg
        --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


Gem files will remain installed in /opt/sensu/embedded/lib/ruby/gems/2.0.0/gems/pg-0.17.1 for inspection.
Results logged to /opt/sensu/embedded/lib/ruby/gems/2.0.0/gems/pg-0.17.1/ext/gem_make.out