diff --git a/ChangeLog b/ChangeLog
index 174075af0a..37d06f020b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Apr 29 10:17:42 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* thread.c (lock_func): small cleanup.
+
 Fri Apr 29 10:07:13 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread.c (rb_mutex_lock, lock_func): Avoid busy loop and
diff --git a/thread.c b/thread.c
index ae4e669d15..8547ff8738 100644
--- a/thread.c
+++ b/thread.c
@@ -3235,10 +3235,15 @@ lock_func(rb_thread_t *th, mutex_t *mutex, int timeout_ms)
 
     native_mutex_lock(&mutex->lock);
     th->transition_for_lock = 0;
-    while (mutex->th || (mutex->th = th, 0)) {
+    for (;;) {
 	struct timespec ts;
 	int ret;
 
+	if (!mutex->th) {
+	    mutex->th = th;
+	    break;
+	}
+
 	mutex->cond_waiting++;
 	if (timeout_ms) {
 	    ts = init_lock_timeout(timeout_ms);