diff --git a/ChangeLog b/ChangeLog
index eaf1e12..da9b262 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-12-16  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* chopstx.c (chx_timer_expired): Bug fix of wake up.
+	(chx_mutex_unlock): Avoid non-deterministic thing.
+
 2017-12-14  NIIBE Yutaka  <gniibe@fsij.org>
 
 	* board/board-st-nucleo-f103.h: Update.
diff --git a/chopstx-cortex-m.c b/chopstx-cortex-m.c
index b983f0c..28f1d3c 100644
--- a/chopstx-cortex-m.c
+++ b/chopstx-cortex-m.c
@@ -287,7 +287,7 @@ chx_request_preemption (uint16_t prio)
  *
  * Returns:
  *          1 on wakeup by others.
- *          0 on normal wakeup.
+ *          0 on normal wakeup (timer expiration, getting lock).
  *         -1 on cancellation.
  */
 static uintptr_t __attribute__ ((naked, noinline))
diff --git a/chopstx.c b/chopstx.c
index ca36560..5585d89 100644
--- a/chopstx.c
+++ b/chopstx.c
@@ -403,6 +403,7 @@ chx_timer_expired (void)
 	       tp = tp_next)
 	    {
 	      next_tick = tp->v;
+	      tp->v = (uintptr_t)0;
 	      tp_next = (struct chx_thread *)tp->next;
 	      ll_dequeue ((struct chx_pq *)tp);
 	      chx_ready_enqueue (tp);
@@ -575,6 +576,7 @@ chx_mutex_unlock (chopstx_mutex_t *mutex)
       uint16_t newprio = running->prio_orig;
       chopstx_mutex_t *m;
 
+      tp->v = (uintptr_t)0;
       chx_ready_enqueue (tp);
 
       /* Examine mutexes we hold, and determine new priority for running.  */