diff --git a/ChangeLog b/ChangeLog
index cd5d22551e..7998c897ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sat Jun 25 23:14:47 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
+
+	* thread.c (rb_threadptr_check_signal): remove unnecessary th->status
+	  backup. fix race condition which may results unexpected main thread's
+	  status transition. see #4072
+
 Fri Jun 24 19:57:30 2011  Hiroshi Nakamura  <nahi@ruby-lang.org>
 
 	* lib/webrick/httprequest.rb (setup_forwarded_info): Parsing request
diff --git a/thread.c b/thread.c
index 9324371d16..e76b5ed99b 100644
--- a/thread.c
+++ b/thread.c
@@ -2953,13 +2953,10 @@ rb_threadptr_check_signal(rb_thread_t *mth)
     /* mth must be main_thread */
 
     if (!mth->exec_signal && (sig = rb_get_next_signal()) > 0) {
-	enum rb_thread_status prev_status = mth->status;
 	thread_debug("main_thread: %s, sig: %d\n",
-		     thread_status_name(prev_status), sig);
+		     thread_status_name(mth->status), sig);
 	mth->exec_signal = sig;
-	if (mth->status != THREAD_KILLED) mth->status = THREAD_RUNNABLE;
 	rb_threadptr_interrupt(mth);
-	mth->status = prev_status;
     }
 }