diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c b/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c
index fb72506126..1651faaab2 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c
@@ -260,8 +260,10 @@ enum rtc_boot_magic check_fast_reboot(void)
 // set RTC register for a fast reboot
 void set_fast_reboot(enum rtc_boot_magic v)
 {
-    uint32_t vv = (uint32_t)v;
-    set_rtc_backup(0, &vv, 1);
+    if (check_fast_reboot() != v) {
+        uint32_t vv = (uint32_t)v;
+        set_rtc_backup(0, &vv, 1);
+    }
 }
 
 #else // NO_FASTBOOT
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h b/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h
index 2705e053f0..d5ad9f7dc1 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h
@@ -58,7 +58,8 @@ enum rtc_boot_magic {
     RTC_BOOT_OFF  = 0,
     RTC_BOOT_HOLD = 0xb0070001,
     RTC_BOOT_FAST = 0xb0070002,
-    RTC_BOOT_CANBL = 0xb0080000 // ORd with 8 bit local node ID
+    RTC_BOOT_CANBL = 0xb0080000, // ORd with 8 bit local node ID
+    RTC_BOOT_FWOK = 0xb0093a26 // indicates FW ran for 30s
 };
     
 // see if RTC registers is setup for a fast reboot