diff --git a/ChangeLog b/ChangeLog
index e997096679..ab04dc467d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Nov 15 18:04:06 2007  Tanaka Akira  <akr@fsij.org>
+
+	* tool/compile_prelude.rb: fix TMP_RUBY_PREFIX for relative load path
+	  environment.
+
 Thu Nov 15 17:28:21 2007  Tanaka Akira  <akr@fsij.org>
 
 	* tool/compile_prelude.rb: absolute path may not start with a slash.
diff --git a/tool/compile_prelude.rb b/tool/compile_prelude.rb
index 7199434441..e792b77406 100644
--- a/tool/compile_prelude.rb
+++ b/tool/compile_prelude.rb
@@ -33,8 +33,7 @@ lines_list = preludes.map {|filename|
       unless mkconf
         require 'rbconfig'
         mkconf = RbConfig::MAKEFILE_CONFIG.merge('prefix'=>'#{TMP_RUBY_PREFIX}')
-        exlen = $:.reverse.find{|e|e!="."}.length - RbConfig::CONFIG["prefix"].length
-        setup_ruby_prefix = "TMP_RUBY_PREFIX = $:.reverse.find{|e|e!=\".\"}[0..#{-exlen-1}]\n"
+        setup_ruby_prefix = "TMP_RUBY_PREFIX = $:.reverse.find{|e|e!=\".\"}.sub(%r{(.*)/lib/.*}m, \"\\\\1\")\n"
         teardown_ruby_prefix = 'Object.class_eval { remove_const "TMP_RUBY_PREFIX" }'
       end
       if RbConfig::MAKEFILE_CONFIG.has_key? key