diff --git a/ChangeLog b/ChangeLog
index 7aafc6f972..3e48e9b16f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jun 27 21:29:50 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* thread_pthread.h (rb_global_vm_lock_struct): add volatile to
+	  gvl->waiting. now thread_timer() access it w/o lock.
+
 Mon Jun 27 21:16:11 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread_pthread.c: s/__gvl_acquire/gvl_acquire_common/ and
diff --git a/thread_pthread.h b/thread_pthread.h
index e693fba299..f180a79d27 100644
--- a/thread_pthread.h
+++ b/thread_pthread.h
@@ -38,7 +38,7 @@ typedef struct rb_global_vm_lock_struct {
     pthread_mutex_t lock;
 
     /* slow path */
-    unsigned long waiting;
+    volatile unsigned long waiting;
     rb_thread_cond_t cond;
 
     /* yield */