diff --git a/ChangeLog b/ChangeLog
index b52fdfe97f..08d7f1f3c4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sat May 17 12:34:54 2008  Yuki Sonoda (Yugui) <yugui@yugui.jp>
+
+	* thread_pthread.c (Init_native_thread): Kernel#.sleep used never to
+	  sleep on Mac OS X. Reported by arton <artonx AT yahoo.co.jp>.
+
+	* thread_pthread.c (native_sleep): added error checks.
+
 Sat May 17 11:29:11 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* file.c (rb_file_s_extname): first dot is not an extension name.
diff --git a/thread_pthread.c b/thread_pthread.c
index 30ffa8ca70..5ea391abd4 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -149,6 +149,7 @@ Init_native_thread(void)
 
     pthread_key_create(&ruby_native_thread_key, NULL);
     th->thread_id = pthread_self();
+    native_cond_initialize(&th->native_thread_data.sleep_cond);
     ruby_thread_set_native(th);
     native_mutex_initialize(&signal_thread_list_lock);
     posix_signal(SIGVTALRM, null_func);
@@ -432,9 +433,11 @@ native_sleep(rb_thread_t *th, struct timeval *tv)
 	}
 	else {
 	    if (tv == 0 || ts.tv_sec < tvn.tv_sec /* overflow */ ) {
+		int r;
 		thread_debug("native_sleep: pthread_cond_wait start\n");
-		pthread_cond_wait(&th->native_thread_data.sleep_cond,
+		r = pthread_cond_wait(&th->native_thread_data.sleep_cond,
 				  &th->interrupt_lock);
+                if (r) rb_bug("pthread_cond_wait: %d", r);
 		thread_debug("native_sleep: pthread_cond_wait end\n");
 	    }
 	    else {
@@ -443,6 +446,8 @@ native_sleep(rb_thread_t *th, struct timeval *tv)
 			     (unsigned long)ts.tv_sec, ts.tv_nsec);
 		r = pthread_cond_timedwait(&th->native_thread_data.sleep_cond,
 					   &th->interrupt_lock, &ts);
+		if (r && r != ETIMEDOUT) rb_bug("pthread_cond_timedwait: %d", r);
+
 		thread_debug("native_sleep: pthread_cond_timedwait end (%d)\n", r);
 	    }
 	}