`gem install activerecord-postgresql-adapter` (pg is not part of the bundle. Add it to Gemfile.) (LoadError)

If you see this error in your heroku logs “`gem install activerecord-postgresql-adapter` (pg is not part of the bundle. Add it to Gemfile.”

/app/vendor/bundle/ruby/1.9.1/gems/bundler-1.3.0.pre.2/lib/bundler/rubygems_integration.rb:177:in `block in replace_gem': Please install the postgresql adapter: `gem install activerecord-postgresql-adapter` (pg is not part of the bundle. Add it to Gemfile.) (LoadError)

Then you must add this to your production section of your Gemfile or create it if you don’t have one:

group :production do
gem 'therubyracer-heroku', '0.8.1.pre3'
gem 'pg'
end