Ubuntu: Installing pg gem

After updating my Ubuntu from 14.04 to 15.04, I ran across problem running "bundle install". It told me to install the pg gem manually. I did, but I got the error below. To fix the problem, I had to install libpg-dev before running bundle install again.

sudo apt-get install libpq-dev

Error

Building native extensions.  This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.

    /home/irobot/.rvm/rubies/ruby-2.2.0/bin/ruby -r ./siteconf20150721-26806-ml2lou.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** 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=/home/irobot/.rvm/rubies/ruby-2.2.0/bin/$(RUBY_BASE_NAME)
    --with-pg
    --without-pg
    --enable-windows-cross
    --disable-windows-cross
    --with-pg-config
    --without-pg-config
    --with-pg_config
    --without-pg_config
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib

extconf failed, exit code 1

Gem files will remain installed in /home/irobot/.rvm/gems/ruby-2.2.0/gems/pg-0.18.2 for inspection.
Results logged to /home/irobot/.rvm/gems/ruby-2.2.0/extensions/x86_64-linux/2.2.0/pg-0.18.2/gem_make.out

Resource:

http://stackoverflow.com/questions/6040583/cant-find-the-libpq-fe-h-header-when-trying-to-install-pg-gem