diff --git a/ChangeLog b/ChangeLog
index 8a3d5fa9e6..38172fc2d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Jun  3 19:47:18 2012  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* thread.c (vm_living_thread_num): suppress a warning.
+
 Sun Jun  3 17:23:52 2012  Tanaka Akira  <akr@fsij.org>
 
 	* use execve() to preserve environment variables when exec method is
diff --git a/thread.c b/thread.c
index 122fe30fd0..609e726620 100644
--- a/thread.c
+++ b/thread.c
@@ -2163,7 +2163,7 @@ thread_keys_i(ID key, VALUE value, VALUE ary)
 static int
 vm_living_thread_num(rb_vm_t *vm)
 {
-    return vm->living_threads->num_entries;
+    return (int)vm->living_threads->num_entries;
 }
 
 int