diff --git a/ChangeLog b/ChangeLog
index 72dc33f732..ac9c411092 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Nov 13 13:05:37 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* prelude.rb (Thread.exclusive): warn as deprecated.
+
 Fri Nov 13 10:36:39 2015  Victor Nawothnig  <Victor.Nawothnig@gmail.com>
 
 	* parse.y (new_unless): optimize constant condition for `unless`
diff --git a/prelude.rb b/prelude.rb
index 20a9e2df10..8a172a22e9 100644
--- a/prelude.rb
+++ b/prelude.rb
@@ -8,6 +8,7 @@ class Thread
   # 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
+    warn "Thread.exclusive is deprecated, use Mutex", caller
     MUTEX_FOR_THREAD_EXCLUSIVE.synchronize{
       yield
     }