diff --git a/ChangeLog b/ChangeLog
index 6d42aa094c..2b838883a7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Aug 29 12:16:47 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/tmpdir.rb (Dir.mktmpdir): rolled back r24699.  [ruby-dev:39193]
+
 Sat Aug 29 03:27:17 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/tempfile.rb (Tempfile#make_tmpname): removed thread race
diff --git a/lib/tmpdir.rb b/lib/tmpdir.rb
index 1b137eeae3..0d247bdd54 100644
--- a/lib/tmpdir.rb
+++ b/lib/tmpdir.rb
@@ -111,10 +111,9 @@ class Dir
     end
     tmpdir ||= Dir.tmpdir
     t = Time.now.strftime("%Y%m%d")
-    th = Thread.current.object_id.to_s(36)
     n = nil
     begin
-      path = "#{tmpdir}/#{prefix}#{t}-#{$$}-#{th}-#{rand(0x100000000).to_s(36)}"
+      path = "#{tmpdir}/#{prefix}#{t}-#{$$}-#{rand(0x100000000).to_s(36)}"
       path << "-#{n}" if n
       path << suffix
       Dir.mkdir(path, 0700)