diff --git a/ChangeLog b/ChangeLog
index 93dba151fe..b78f7d2c05 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+Sat Mar 13 00:11:05 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ruby.c (ruby_init_loadpath_safe): mark initial load paths.
+
+	* gem_prelude.rb (push_all_highest_version_gems_on_load_path):
+	  search insertion position by initial load path mark.
+
+	* lib/rubygems.rb (Gem.load_path_insert_index): ditto.
+
 Fri Mar 12 21:34:00 2010  Kenta Murata  <mrkn@mrkn.jp>
 
 	* NEWS: emoji encodings.
diff --git a/gem_prelude.rb b/gem_prelude.rb
index fac6a3806a..5928356afa 100644
--- a/gem_prelude.rb
+++ b/gem_prelude.rb
@@ -267,7 +267,7 @@ if defined?(Gem) then
           require_paths.first.instance_variable_set(:@gem_prelude_index, true)
         end
         # gem directories must come after -I and ENV['RUBYLIB']
-        $:[$:.index(ConfigMap[:sitelibdir]),0] = require_paths
+        $:[$:.index{|e|e.instance_variable_defined?(:@gem_prelude_index)}||-1,0] = require_paths
       end
 
       def const_missing(constant)
diff --git a/lib/rubygems.rb b/lib/rubygems.rb
index dd086bc821..d0c82970eb 100644
--- a/lib/rubygems.rb
+++ b/lib/rubygems.rb
@@ -254,8 +254,6 @@ module Gem
       File.join spec.full_gem_path, path
     end
 
-    sitelibdir = ConfigMap[:sitelibdir]
-
     # gem directories must come after -I and ENV['RUBYLIB']
     insert_index = load_path_insert_index
 
@@ -570,23 +568,9 @@ module Gem
 
   ##
   # The index to insert activated gem paths into the $LOAD_PATH.
-  #
-  # Defaults to the site lib directory unless gem_prelude.rb has loaded paths,
-  # then it inserts the activated gem's paths before the gem_prelude.rb paths
-  # so you can override the gem_prelude.rb default $LOAD_PATH paths.
 
   def self.load_path_insert_index
-    index = $LOAD_PATH.index ConfigMap[:sitelibdir]
-
-    $LOAD_PATH.each_with_index do |path, i|
-      if path.instance_variables.include?(:@gem_prelude_index) or
-        path.instance_variables.include?('@gem_prelude_index') then
-        index = i
-        break
-      end
-    end
-
-    index
+    $LOAD_PATH.index {|path| path.instance_variable_defined?(:@gem_prelude_index)}
   end
 
   ##
diff --git a/ruby.c b/ruby.c
index fdca44593d..bf0f83d67c 100644
--- a/ruby.c
+++ b/ruby.c
@@ -339,6 +339,7 @@ void
 ruby_init_loadpath_safe(int safe_level)
 {
     VALUE load_path;
+    ID id_initial_load_path_mark;
     extern const char ruby_initial_load_paths[];
     const char *paths = ruby_initial_load_paths;
 #if defined LOAD_RELATIVE
@@ -432,16 +433,18 @@ ruby_init_loadpath_safe(int safe_level)
 #define RUBY_RELATIVE(path, len) rubylib_mangled_path(path, len)
 #define PREFIX_PATH() rubylib_mangled_path(RUBY_LIB_PREFIX, sizeof(RUBY_LIB_PREFIX)-1)
 #endif
-#define incpush(path) rb_ary_push(load_path, (path))
     load_path = GET_VM()->load_path;
 
     if (safe_level == 0) {
 	ruby_push_include(getenv("RUBYLIB"), identical_path);
     }
 
+    id_initial_load_path_mark = rb_intern_const("@gem_prelude_index");
     while (*paths) {
 	size_t len = strlen(paths);
-	incpush(RUBY_RELATIVE(paths, len));
+	VALUE path = RUBY_RELATIVE(paths, len);
+	rb_ivar_set(path, id_initial_load_path_mark, path);
+	rb_ary_push(load_path, path);
 	paths += len + 1;
     }
 
diff --git a/tool/compile_prelude.rb b/tool/compile_prelude.rb
index d13670d955..93a6dd9cf0 100755
--- a/tool/compile_prelude.rb
+++ b/tool/compile_prelude.rb
@@ -48,7 +48,7 @@ class Prelude
         key = $1
         unless @mkconf
           require './rbconfig'
-          @mkconf = RbConfig::MAKEFILE_CONFIG.merge('rubylibprefix'=>'#{TMP_RUBY_PREFIX}')
+          @mkconf = RbConfig::MAKEFILE_CONFIG.merge('prefix'=>'#{TMP_RUBY_PREFIX}')
         end
         if RbConfig::MAKEFILE_CONFIG.has_key? key
           val = RbConfig.expand("$(#{key})", @mkconf)