Issue with Sqlite3 on Ubuntu

I have installed sqlite3, libsqlite3-dev and libsqlite3-ruby

When I run "sudo gem1.8 install sqlite3-ruby"
I get the following:

Building native extensions. This could take a while...
ERROR: Error installing sqlite3-ruby:
        ERROR: Failed to build gem native extension.

/usr/bin/ruby1.8 extconf.rb install sqlite3-ruby
extconf.rb:1:in `require': no such file to load -- mkmf (LoadError)
        from extconf.rb:1

Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/sqlite3-
ruby-1.2.4 for inspection.
Results logged to /usr/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.2.4/ext/

Any ideas?

sounds like you're missing the ruby-dev package