diff --git a/ChangeLog b/ChangeLog
index 5eef2f1cc7..6d42aa094c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,8 +1,10 @@
-Sat Aug 29 03:11:29 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Sat Aug 29 03:27:17 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/tempfile.rb (Tempfile#make_tmpname): removed thread race
 	  condition.
 
+	* lib/tmpdir.rb (Dir.mktmpdir): ditto.
+
 Fri Aug 28 20:29:34 2009  Akinori MUSHA  <knu@iDaemons.org>
 
 	* lib/tempfile.rb (Tempfile#callback): Debug information should be
diff --git a/lib/tmpdir.rb b/lib/tmpdir.rb
index 0d247bdd54..1b137eeae3 100644
--- a/lib/tmpdir.rb
+++ b/lib/tmpdir.rb
@@ -111,9 +111,10 @@ 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}-#{$$}-#{rand(0x100000000).to_s(36)}"
+      path = "#{tmpdir}/#{prefix}#{t}-#{$$}-#{th}-#{rand(0x100000000).to_s(36)}"
       path << "-#{n}" if n
       path << suffix
       Dir.mkdir(path, 0700)