foo.diff

diff --git i/Rakefile w/Rakefile
index d1bbfa6..ecf10bb 100644
--- i/Rakefile
+++ w/Rakefile
@@ -52,7 +52,7 @@ end
 
 load_configuration
 
-unless BUILD_CONFIG[:config_version] == 179
+unless BUILD_CONFIG[:config_version] == 180
   STDERR.puts "Your configuration is outdated, please run ./configure first"
   exit 1
 end
diff --git i/configure w/configure
index ec2fee9..fd8d791 100755
--- i/configure
+++ w/configure
@@ -140,7 +140,7 @@ class Configure
     @release_date = validate_release_date
 
     # Configure settings
-    @config_version = 179
+    @config_version = 180
     @run_bundle = true
     @fetch_gems = true
   end
@@ -1720,7 +1720,8 @@ int main() { return tgetnum(""); }
       :build_tool_gems    => @build_tool_gems,
       :build_c_ext_gems   => @build_c_ext_gems,
       :rubygems_gems      => @rubygems_gems,
-      :runtime_gems       => @runtime_gems
+      :runtime_gems       => @runtime_gems,
+      :default_gems       => @default_gems
     }
 
     write_config_rb @config, config_settings
@@ -2031,7 +2032,7 @@ required to run it.
   def unpack_gems
     @log.write "\nUnpacking bootstrap gems..."
 
-    gems = @build_tool_gems + @build_c_ext_gems + @rubygems_gems
+    gems = @default_gems = @build_tool_gems + @build_c_ext_gems + @rubygems_gems
 
     runtime_gems = File.expand_path "../runtime/gems", __FILE__
     FileUtils.mkdir_p runtime_gems unless File.directory? runtime_gems
diff --git i/rakelib/preinstall_gems.rb w/rakelib/preinstall_gems.rb
index acdd4bd..d290eb7 100644
--- i/rakelib/preinstall_gems.rb
+++ w/rakelib/preinstall_gems.rb
@@ -1,9 +1,11 @@
 require 'rubygems'
 require 'rubygems/dependency_installer'
 require 'rubinius/build_config'
+require 'fileutils'
 
 puts "Pre-installing gems for #{RUBY_VERSION}..."
 
+default_gems = Rubinius::BUILD_CONFIG[:default_gems]
 gems = Rubinius::BUILD_CONFIG[:runtime_gems]
 options = {
   :wrappers             => true,
@@ -14,6 +16,23 @@ options = {
   :conservative         => true
 }
 
+FileUtils.mkdir_p Gem::Specification.default_specifications_dir
+default_gems.each do |name, version|
+  name_re = /#{name}/
+  version_req = Gem::Requirement.create "~> #{version}"
+  unless Gem::Specification.any? { |s| s.name =~ name_re and version_req =~ s.version }
+    gem = Dir["#{name}-#{version}*"].first
+    s = Gem::Installer.new(gem).spec
+    spec_file = File.join(Gem::Specification.default_specifications_dir, "#{s.full_name}.gemspec")
+
+    File.open(spec_file, "w") do |f|
+      f.puts s.to_ruby_for_cache
+    end
+
+    puts "Wrote gemspec for #{s.name} #{s.version}"
+  end
+end
+
 gems.each do |name, version|
   name_re = /#{name}/
   version_req = Gem::Requirement.create "~> #{version}"