require fails with undefined symbol

I have installed wxruby via gems on Ubuntu 7.10 but running sample/minimal.rb fails:

ruby -rubygems minimal.rb

/var/lib/gems/1.8/gems/wxruby-1.9.8-x86-linux/lib/wxruby2.so:
/var/lib/gems/1.8/gems/wxruby-1.9.8-x86-linux/lib/wxruby2.so: undefined symbol:
g_assertion_message_expr - /var/lib/gems/1.8/gems/wxruby-1.9.8-x86-linux/lib/wxruby2.so (LoadError)
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:32:in `require'
        from /var/lib/gems/1.8/gems/wxruby-1.9.8-x86-linux/lib/wx.rb:12
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:32:in `gem_original_require'
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:32:in `require'
        from minimal.rb:8

Any help (hopefully without recourse to source compilation) would be very welcome.

Thanks, Richard W