Error installing sqlite3 gem on solaris

I am attempting to install the sqlite3 gem under Solaris and am getting
the
following error:


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

/opt/csw/bin/ruby 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
/opt/csw/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.2.4 for inspection.
Results logged to
/opt/csw/lib/ruby/gems/1.8/gems/sqlite3-ruby-1.2.4/ext/sqlite3_api/gem_make.out

How do I fix this?

/opt/csw/bin/ruby extconf.rb install sqlite3-ruby
extconf.rb:1:in `require’: no such file to load – mkmf (LoadError)
from extconf.rb:1

Looks like your ruby is somehow installed wrong since that should be
available.
=r