Cannot install pg gem in Mavericks with Postgres.app

I am trying to install the pg gem for use with Postgres.app on my local machine. I am running Mavericks.

Postgres.app is installed and running fine, but I cannot get the gem to work. I've done the following:

1. Used the command 'env ARCHFLAGS="-arch x86_64" gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/MacOS/bin/pg_config' from the Postgres.app documentation
2. Updated Homebrew and installed the Apple GCC 4.2
3. Installed the Xcode developer tools
4. Updated my $PATH to reference both the Postgres.app bin and lib directories

All with no success. Here is the specific error message I receive:

Building native extensions with: '--with-pg-config=/Applications/Postgres.app/Contents/MacOS/bin/pg_config'
This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.

    /Users/Brian/.rvm/rubies/ruby-2.0.0-p353/bin/ruby extconf.rb --with-pg-config=/Applications/Postgres.app/Contents/MacOS/bin/pg_config
Using config values from /Applications/Postgres.app/Contents/MacOS/bin/pg_config
sh: /Applications/Postgres.app/Contents/MacOS/bin/pg_config: No such file or directory
sh: /Applications/Postgres.app/Contents/MacOS/bin/pg_config: No such file or directory
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
    --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=/Users/Brian/.rvm/rubies/ruby-2.0.0-p353/bin/ruby
    --with-pg
    --without-pg
    --with-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}/

I'd appreciate any help you can offer. Thanks!

You probably have the wrong path for --with-pg-config, check if it's actually there.

You can find the correct path to pg_config with:

find /Applications -name pg_config

In the latest Postgres.app Version the path is:

gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/Versions/9.5/bin/pg_config

In my case (running Postgres.app v9.3.4.2) it only seemed to work when prepending the environment architecture flags:

env ARCHFLAGS="-arch x86_64" gem install pg -- \
--with-pg-config=/Applications/Postgres.app/Contents/Versions/9.3/bin/pg_config