Could not find a JavaScript runtime -- Bundler & Rbenv

I'm trying to deploy my app using Capistrano, Bundler, and Rbenv. When I
execute "cap deploy:update" I get get the following error when trying to
precompile:

"Could not find a JavaScript runtime. See
https://github.com/sstephenson/execjs for a list of available runtimes."

failed: "env
PATH=$HOME/.rbenv/shims:$HOME/.rbenv/bin:$HOME/.rbenv/versions/1.9.3-p125/bin:/home/ari/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems:$PATH
sh -c 'cd /home/ari/www/tutelage/releases/20120504012619 && bundle exec
rake RAILS_ENV=production RAILS_GROUPS=assets assets:precompile'" on
prodserv1

Does anyone know why? My Gemfile includes: execjs and therubyracer

My deploy.rb file includes:

require 'bundler/capistrano'

load 'deploy/assets'

default_run_options[:pty] = true

set :default_environment, { "PATH" =>
"$HOME/.rbenv/shims:$HOME/.rbenv/bin:$HOME/.rbenv/versions/1.9.3-p125/bin:$HOME/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems:$PATH"
}

Thanks.

Ari

AFAIK execjs and rubyracer are not JS runtimes themselves, only
wrappers (though I may be wrong!). I got this error too, installed
NodeJS on my server, and everything worked perfectly, so I made a
conclusion, that NodeJS is suitable JS runtime for Rails:)))