diff --git a/ChangeLog b/ChangeLog
index cd9c6f110a..0aebdc1aa9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+Sun Jan  4 17:07:45 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/rubygems.rb (Gem.set_home, Gem.set_paths): should not create
+	  directories stealthily.  [ruby-core:20990]
+
+	* lib/rubygems.rb (Gem.find_home): expand_path deals with platform
+	  dependent envirionments.
+
+	* lib/rdoc/ri/paths.rb (RDoc::HOMEDIR): ditto.
+
+	* instruby.rb (gem): creates gem directories at installation.
+
 Sun Jan  4 15:41:37 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* encoding.c (rb_filesystem_encoding, rb_locale_charmap): uses
diff --git a/instruby.rb b/instruby.rb
index 38ed40c52b..ea9ef2a582 100755
--- a/instruby.rb
+++ b/instruby.rb
@@ -409,6 +409,13 @@ install?(:local, :comm, :man) do
   end
 end
 
+install?(:local, :comm, :gem) do
+  puts "creating default gem directories"
+
+  gpath = Gem.default_dir
+  makedirs Gem::DIRECTORIES.collect {|dir| File.join(gpath, dir)}
+end
+
 $install << :local << :ext if $install.empty?
 $install.each do |inst|
   if !(procs = $install_procs[inst]) || procs.empty?
diff --git a/lib/rdoc/ri/paths.rb b/lib/rdoc/ri/paths.rb
index 2f72b9dfd5..fcafb279fd 100644
--- a/lib/rdoc/ri/paths.rb
+++ b/lib/rdoc/ri/paths.rb
@@ -31,13 +31,7 @@ module RDoc::RI::Paths
   base    = File.join(RbConfig::CONFIG['datadir'], "ri", VERSION)
   SYSDIR  = File.join(base, "system")
   SITEDIR = File.join(base, "site")
-  homedir = ENV['HOME'] || ENV['USERPROFILE'] || ENV['HOMEPATH']
-
-  if homedir then
-    HOMEDIR = File.join(homedir, ".rdoc")
-  else
-    HOMEDIR = nil
-  end
+  HOMEDIR = (File.expand_path("~/.rdoc") rescue nil)
 
   begin
     require 'rubygems' unless defined?(Gem) and defined?(Gem::Enable) and
diff --git a/lib/rubygems.rb b/lib/rubygems.rb
index 9913b59ce1..77930016fa 100644
--- a/lib/rubygems.rb
+++ b/lib/rubygems.rb
@@ -373,22 +373,12 @@ module Gem
   #   least on Win32).
 
   def self.find_home
-    ['HOME', 'USERPROFILE'].each do |homekey|
-      return ENV[homekey] if ENV[homekey]
-    end
-
-    if ENV['HOMEDRIVE'] && ENV['HOMEPATH'] then
-      return "#{ENV['HOMEDRIVE']}#{ENV['HOMEPATH']}"
-    end
-
-    begin
-      File.expand_path("~")
-    rescue
-      if File::ALT_SEPARATOR then
-          "C:/"
-      else
-          "/"
-      end
+    File.expand_path("~")
+  rescue
+    if File::ALT_SEPARATOR then
+      "C:/"
+    else
+      "/"
     end
   end
 
@@ -691,7 +681,6 @@ module Gem
   def self.set_home(home)
     home = home.gsub(File::ALT_SEPARATOR, File::SEPARATOR) if File::ALT_SEPARATOR
     @gem_home = home
-    ensure_gem_subdirectories(@gem_home)
   end
 
   private_class_method :set_home
@@ -716,16 +705,6 @@ module Gem
     end
 
     @gem_path.uniq!
-    @gem_path.each do |path|
-      if 0 == File.expand_path(path).index(Gem.user_home)
-        next unless File.directory? Gem.user_home
-        unless win_platform? then
-          # only create by matching user
-          next if Etc.getpwuid.uid != File::Stat.new(Gem.user_home).uid
-        end
-      end
-      ensure_gem_subdirectories path
-    end
   end
 
   private_class_method :set_paths