diff --git a/sched/sched/sched_timerexpiration.c b/sched/sched/sched_timerexpiration.c
index bfa12099fe..fa26a0cc25 100644
--- a/sched/sched/sched_timerexpiration.c
+++ b/sched/sched/sched_timerexpiration.c
@@ -106,6 +106,24 @@ static unsigned int g_timer_interval;
  * Private Functions
  ****************************************************************************/
 
+static inline_function void set_g_time_tick(clock_t tick)
+{
+#ifdef CONFIG_SYSTEM_TIME64
+  atomic64_set((FAR atomic64_t *)&g_timer_tick, tick);
+#else
+  atomic_set((FAR atomic_t *)&g_timer_tick, tick);
+#endif
+}
+
+static inline_function clock_t get_g_time_tick(void)
+{
+#ifdef CONFIG_SYSTEM_TIME64
+  return atomic64_read((FAR atomic64_t *)&g_timer_tick);
+#else
+  return atomic_read((FAR atomic_t *)&g_timer_tick);
+#endif
+}
+
 #if !defined(CONFIG_SCHED_TICKLESS_TICK_ARGUMENT) && !defined(CONFIG_CLOCK_TIMEKEEPING)
 int up_timer_gettick(FAR clock_t *ticks)
 {
@@ -377,6 +395,7 @@ static clock_t nxsched_timer_process(clock_t ticks, clock_t elapsed,
 
 static clock_t nxsched_timer_start(clock_t ticks, clock_t interval)
 {
+  irqstate_t flags;
   int ret;
 
   if (interval > 0)
@@ -388,6 +407,8 @@ static clock_t nxsched_timer_start(clock_t ticks, clock_t interval)
         }
 #endif
 
+      flags = enter_critical_section();
+
 #ifdef CONFIG_SCHED_TICKLESS_ALARM
       /* Convert the delay to a time in the future (with respect
        * to the time when last stopped the timer).
@@ -400,6 +421,8 @@ static clock_t nxsched_timer_start(clock_t ticks, clock_t interval)
       ret = up_timer_tick_start(interval);
 #endif
 
+      leave_critical_section(flags);
+
       if (ret < 0)
         {
           serr("ERROR: up_timer_start/up_alarm_start failed: %d\n", ret);
@@ -439,22 +462,18 @@ void nxsched_alarm_tick_expiration(clock_t ticks)
 {
   clock_t elapsed;
   clock_t nexttime;
-  irqstate_t flags;
 
   /* Save the time that the alarm occurred */
 
-  flags = enter_critical_section();
-  elapsed = ticks - g_timer_tick;
-  g_timer_tick = ticks;
-  leave_critical_section(flags);
+  elapsed = ticks - get_g_time_tick();
+  set_g_time_tick(ticks);
 
   /* Process the timer ticks and set up the next interval (or not) */
 
   nexttime = nxsched_timer_process(ticks, elapsed, false);
 
-  flags = enter_critical_section();
-  g_timer_interval = nxsched_timer_start(ticks, nexttime);
-  leave_critical_section(flags);
+  elapsed = nxsched_timer_start(ticks, nexttime);
+  atomic_set((FAR atomic_t *)&g_timer_interval, elapsed);
 }
 
 void nxsched_alarm_expiration(FAR const struct timespec *ts)
@@ -490,23 +509,19 @@ void nxsched_timer_expiration(void)
   clock_t ticks;
   clock_t elapsed;
   clock_t nexttime;
-  irqstate_t flags;
 
   /* Get the interval associated with last expiration */
 
-  flags = enter_critical_section();
   up_timer_gettick(&ticks);
-  g_timer_tick = ticks;
-  elapsed = g_timer_interval;
-  leave_critical_section(flags);
+  set_g_time_tick(ticks);
+  elapsed = atomic_read((FAR atomic_t *)&g_timer_interval);
 
   /* Process the timer ticks and set up the next interval (or not) */
 
   nexttime = nxsched_timer_process(ticks, elapsed, false);
 
-  flags = enter_critical_section();
-  g_timer_interval = nxsched_timer_start(ticks, nexttime);
-  leave_critical_section(flags);
+  elapsed = nxsched_timer_start(ticks, nexttime);
+  atomic_set((FAR atomic_t *)&g_timer_interval, elapsed);
 }
 #endif
 
@@ -565,13 +580,15 @@ void nxsched_reassess_timer(void)
 
   /* Convert this to the elapsed time and update clock tickbase */
 
-  elapsed = ticks - g_timer_tick;
-  g_timer_tick = ticks;
+  elapsed = ticks - get_g_time_tick();
+  set_g_time_tick(ticks);
 
   /* Process the timer ticks and start next timer */
 
   nexttime = nxsched_timer_process(ticks, elapsed, true);
-  g_timer_interval = nxsched_timer_start(ticks, nexttime);
+
+  elapsed = nxsched_timer_start(ticks, nexttime);
+  atomic_set((FAR atomic_t *)&g_timer_interval, elapsed);
 }
 
 /****************************************************************************
@@ -590,12 +607,10 @@ void nxsched_reassess_timer(void)
 
 clock_t nxsched_get_next_expired(void)
 {
-  irqstate_t flags;
   sclock_t ret;
 
-  flags = enter_critical_section();
-  ret = g_timer_tick + g_timer_interval - clock_systime_ticks();
-  leave_critical_section(flags);
+  ret = get_g_time_tick() + atomic_read((FAR atomic_t *)&g_timer_interval) -
+        clock_systime_ticks();
 
   return ret < 0 ? 0 : ret;
 }