Buildr fails with rubygems 1.3.6

Buildr fails with rubygems 1.3.6 installed,

boisvert@smudge:~/tmp/buildr$ buildr
(in /home/boisvert/tmp/buildr, development)
Buildr aborted!
undefined method `version=' for #<Gem::Version "0">
/home/boisvert/tmp/buildr/Buildfile:3
(See full trace by running task with --trace)

or here's another failure variation,

boisvert@smudge:~/tmp/buildr-scala$ ~/svn/buildr-clean/_buildr
/home/boisvert/svn/buildr-clean/_buildr:24:Warning: Gem::Dependency#version_requirements is deprecated and will be removed on or after August 2010. Use #requirement
/usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2504:in `const_missing': uninitialized constant Gem::Requirement::OP_RE (NameError)
from /home/boisvert/svn/buildr-clean/lib/buildr/packaging/version_requirement.rb:24
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
from /home/boisvert/svn/buildr-clean/lib/buildr/packaging/artifact_namespace.rb:17
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
from /home/boisvert/svn/buildr-clean/lib/buildr/packaging/artifact.rb:19
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
from /home/boisvert/svn/buildr-clean/lib/buildr/packaging.rb:17
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
from /home/boisvert/svn/buildr-clean/lib/buildr.rb:21
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
from /home/boisvert/svn/buildr-clean/_buildr:28