install failed with "ERROR: Failed to build gem native extension"

[Deleted user]

sudo gem install google
[sudo] password for user: 
Building native extensions.  This could take a while...
ERROR:  Error installing google:
    ERROR: Failed to build gem native extension.

        /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:1:in `<main>'


Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-1.7.3 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/json-1.7.3/ext/json/ext/parser/gem_make.out

[Kerrick]

That's actually a failure in installing the json gem, which is a dependency for my google gem. You may want to open an issue there.

[Deleted user]

Duly noted. Here's the new thread: ruby/json#136