diff --git a/drivers/timers/arch_rtc.c b/drivers/timers/arch_rtc.c
index 3db1173191..8325dff5dc 100644
--- a/drivers/timers/arch_rtc.c
+++ b/drivers/timers/arch_rtc.c
@@ -67,8 +67,12 @@ volatile bool g_rtc_enabled = false;
 
 void up_rtc_set_lowerhalf(FAR struct rtc_lowerhalf_s *lower)
 {
-  g_rtc_lower = lower;
+  g_rtc_lower   = lower;
   g_rtc_enabled = true;
+
+#ifdef CONFIG_RTC_EXTERNAL
+  clock_synchronize();
+#endif
 }
 
 /************************************************************************************