Index: tool/rbinstall.rb
===================================================================
--- tool/rbinstall.rb	(revision 31888)
+++ tool/rbinstall.rb	(working copy)
@@ -532,13 +532,7 @@
 end
 
 install?(:ext, :comm, :gem) do
-  directories = []
-  IO.foreach(File.join(srcdir, "lib/rubygems.rb")) do |line|
-    if /^\s*DIRECTORIES\s*=\s*%w\[(.*?)\]/ =~ line
-      directories = $1.split
-      break
-    end
-  end
+  directories = %w[cache doc gems specifications]
   gpath = CONFIG["sitelibdir"].sub(%r'/site_ruby/(?=[^/]+)', '/gems/')
   prepare "default gems", gpath, directories