RUBYGEMS install on AIX zlib not found

I read all the posts on zlib but cannot find an answer ... .
I installed ruby on AIX 4.3.3 from tar.gz. My ext/zlib contains zlib.o
and zlib.so. make test produces no errors. However, when I run ruby
setup.rb from rubygems install, I get "no such file ..."

Please help me install zlib in the proper place.

/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:21:in
`require__': no such file to load -- zlib (LoadError)
        from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:21:in
`require'
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/package.rb:9
        from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:21:in
`require'
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/builder.rb:1
        from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:21:in
`require'
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems.rb:61:in
`manage_gems'
        from /tmp/rubygems-0.8.11/./post-install.rb:64:in
`install_sources'
        from /tmp/rubygems-0.8.11/./post-install.rb:75:in `try_run_hook'
        from setup.rb:577:in `run_hook'
        from setup.rb:1315:in `exec_task_traverse'
        from setup.rb:1168:in `exec_install'
        from setup.rb:887:in `exec_install'
        from setup.rb:705:in `invoke'
        from setup.rb:674:in `invoke'
        from setup.rb:1352

···

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