bcrypt install issue

Installing bcrypt-ruby (2.1.4) with native extensions /usr/lib/ruby/1.9.1/rubygems/installer.rb:562:in `rescue in block in build_extensions': ERROR: Failed to build gem native extension. (Gem::Installer::ExtensionBuildError)

        /usr/bin/ruby1.9.1 extconf.rb 
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from extconf.rb:13:in `<main>'


Gem files will remain installed in /home/vagrant/.bundler/tmp/31895/gems/bcrypt-ruby-2.1.4 for inspection.
Results logged to /home/vagrant/.bundler/tmp/31895/gems/bcrypt-ruby-2.1.4/ext/mri/gem_make.out
	from /usr/lib/ruby/1.9.1/rubygems/installer.rb:540:in `block in build_extensions'
	from /usr/lib/ruby/1.9.1/rubygems/installer.rb:515:in `each'
	from /usr/lib/ruby/1.9.1/rubygems/installer.rb:515:in `build_extensions'
	from /usr/lib/ruby/1.9.1/rubygems/installer.rb:180:in `install'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/source.rb:96:in `install'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/installer.rb:55:in `block in run'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/spec_set.rb:12:in `block in each'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/spec_set.rb:12:in `each'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/spec_set.rb:12:in `each'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/installer.rb:44:in `run'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/installer.rb:8:in `install'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/cli.rb:226:in `install'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/vendor/thor/task.rb:22:in `run'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/vendor/thor/invocation.rb:118:in `invoke_task'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/vendor/thor.rb:246:in `dispatch'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/lib/bundler/vendor/thor/base.rb:389:in `start'
	from /var/lib/gems/1.9.1/gems/bundler-1.0.10/bin/bundle:13:in `<top (required)>'
	from /usr/local/bin/bundle:23:in `load'
	from /usr/local/bin/bundle:23:in `<main>'
vagrant@localhost:/rms$ ruby --version
ruby 1.9.3p484 (2013-11-22 revision 43786) [x86_64-linux]
vagrant@localhost:/rms$ sudo apt-get install ruby-dev