--- a/tool/rbinstall.rb
+++ b/tool/rbinstall.rb
@@ -714,15 +714,15 @@
   directories = Gem.ensure_gem_subdirectories(gem_dir, :mode => $dir_mode)
   prepare "bundle gems", gem_dir, directories
   Dir.glob(srcdir+'/gems/*.gem').each do |gem|
-    Gem.install gem, Gem::Requirement.default, :install_dir => with_destdir(Gem.dir), :domain => :local, :ignore_dependencies => true
+    Gem.install gem, Gem::Requirement.default, :install_dir => with_destdir(gem_dir), :domain => :local, :ignore_dependencies => true
     gemname = Pathname(gem).basename
     puts "#{" "*30}#{gemname}"
   end
   # fix directory permissions
   # TODO: Gem.install should accept :dir_mode option or something
-  File.chmod($dir_mode, *Dir.glob(with_destdir(Gem.dir)+"/**/"))
+  File.chmod($dir_mode, *Dir.glob(with_destdir(gem_dir)+"/**/"))
   # fix .gemspec permissions
-  File.chmod($data_mode, *Dir.glob(with_destdir(Gem.dir)+"/specifications/*.gemspec"))
+  File.chmod($data_mode, *Dir.glob(with_destdir(gem_dir)+"/specifications/*.gemspec"))
 end

 parse_args()