diff --git a/ChangeLog b/ChangeLog
index a0ec66fc21..1cbedd5ce3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Sep 23 22:58:57 2009  Tanaka Akira  <akr@fsij.org>
+
+	* lib/thread.rb (ConditionVariable#wait): add timeout argument.
+	  [ruby-talk:346154]
+
 Wed Sep 23 21:25:20 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/bigdecimal/lib/bigdecimal/math.rb (atan): refined.
diff --git a/NEWS b/NEWS
index a384402980..3adf36ec6e 100644
--- a/NEWS
+++ b/NEWS
@@ -230,6 +230,10 @@ with all sufficient information, see the ChangeLog file.
   * incompatible changes:
     * Time.parse raises ArgumentError when no date information.
 
+* thread
+  * extended method:
+    * ConditionVariable#wait takes timeout argument.
+
 * securerandom
   * new methods:
     * SecureRandom.urlsafe_base64
diff --git a/lib/thread.rb b/lib/thread.rb
index cb6d8c62fc..34c2a506d2 100644
--- a/lib/thread.rb
+++ b/lib/thread.rb
@@ -59,13 +59,16 @@ class ConditionVariable
   #
   # Releases the lock held in +mutex+ and waits; reacquires the lock on wakeup.
   #
-  def wait(mutex)
+  # If +timeout+ is given, this method returns after +timeout+ seconds passed,
+  # even if no other thread doesn't signal.
+  #
+  def wait(mutex, timeout=nil)
     begin
       # TODO: mutex should not be used
       @waiters_mutex.synchronize do
         @waiters.push(Thread.current)
       end
-      mutex.sleep
+      mutex.sleep timeout
     end
   end