diff --git a/ports/nrf/common-hal/rtc/RTC.c b/ports/nrf/common-hal/rtc/RTC.c
index 9f56f2f0df..06345f5895 100644
--- a/ports/nrf/common-hal/rtc/RTC.c
+++ b/ports/nrf/common-hal/rtc/RTC.c
@@ -34,11 +34,28 @@
 #include "supervisor/shared/translate.h"
 
 // This is the time in seconds since 2000 that the RTC was started.
-static uint32_t rtc_offset = 0;
+__attribute__((section(".uninitialized"))) static uint32_t rtc_offset[3];
+
+// These values are placed before and after the current RTC count.  They are
+// used to determine if the RTC count is valid.  These randomly-generated values
+// will be set when the RTC value is set in order to mark the RTC as valid. If
+// the system crashes or reboots, these values will remain undisturbed and the
+// RTC offset will remain valid.
+//
+// If Circuit Python is updated or these symbols shift around, the prefix and
+// suffix will no longer match, and the time will no longer be valid.
+#define RTC_OFFSET_CHECK_PREFIX 0x25ea7e2a
+#define RTC_OFFSET_CHECK_SUFFIX 0x2b80b69e
+
+void common_hal_rtc_init(void) {
+    // If the prefix and suffix are not valid, zero-initialize the RTC offset.
+    if ((rtc_offset[0] != RTC_OFFSET_CHECK_PREFIX) || (rtc_offset[2] != RTC_OFFSET_CHECK_SUFFIX))
+        rtc_offset[1] = 0;
+}
 
 void common_hal_rtc_get_time(timeutils_struct_time_t *tm) {
     uint64_t ticks_s = port_get_raw_ticks(NULL) / 1024;
-    timeutils_seconds_since_2000_to_struct_time(rtc_offset + ticks_s, tm);
+    timeutils_seconds_since_2000_to_struct_time(rtc_offset[1] + ticks_s, tm);
 }
 
 void common_hal_rtc_set_time(timeutils_struct_time_t *tm) {
@@ -46,7 +63,13 @@ void common_hal_rtc_set_time(timeutils_struct_time_t *tm) {
     uint32_t epoch_s = timeutils_seconds_since_2000(
         tm->tm_year, tm->tm_mon, tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec
     );
-    rtc_offset = epoch_s - ticks_s;
+    rtc_offset[1] = epoch_s - ticks_s;
+
+    // Set the prefix and suffix in order to indicate the time is valid.  This
+    // must be done after the offset is updated, in case there is a crash or
+    // power failure.
+    rtc_offset[0] = RTC_OFFSET_CHECK_PREFIX;
+    rtc_offset[2] = RTC_OFFSET_CHECK_SUFFIX;
 }
 
 int common_hal_rtc_get_calibration(void) {
diff --git a/ports/nrf/common-hal/rtc/RTC.h b/ports/nrf/common-hal/rtc/RTC.h
index 0207c8338c..e51f1f7848 100644
--- a/ports/nrf/common-hal/rtc/RTC.h
+++ b/ports/nrf/common-hal/rtc/RTC.h
@@ -29,5 +29,6 @@
 
 extern void rtc_init(void);
 extern void rtc_reset(void);
+extern void common_hal_rtc_init(void);
 
 #endif  // MICROPY_INCLUDED_NRF_COMMON_HAL_RTC_RTC_H