diff --git a/ChangeLog b/ChangeLog
index 29f7e6b451..15be522d6a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Apr 17 16:28:10 2014  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
+
+	* prelude.rb: [DOC] Update Thread::exclusive docs by @stevenharman.
+
 Thu Apr 17 10:03:53 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/fileutils.rb (FileUtils#copy_entry): update rdoc about
diff --git a/prelude.rb b/prelude.rb
index 2b371e7134..cc24a81474 100644
--- a/prelude.rb
+++ b/prelude.rb
@@ -4,9 +4,9 @@ class Thread
   # call-seq:
   #    Thread.exclusive { block }   => obj
   #
-  # Wraps a block in Thread.critical, restoring the original value
-  # upon exit from the critical section, and returns the value of the
-  # block.
+  # Wraps the block in a single, VM-global Mutex.synchronize, returning the
+  # value of the block. A thread executing inside the exclusive section will
+  # only block other threads which also use the Thread.exclusive mechanism.
   def self.exclusive
     MUTEX_FOR_THREAD_EXCLUSIVE.synchronize{
       yield