diff --git a/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.c b/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.c
index 6d44570f1..a6c776d3a 100644
--- a/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.c
+++ b/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.c
@@ -512,7 +512,8 @@ void rtcSTM32SetPeriodicWakeup(RTCDriver *rtcp, const RTCWakeup *wakeupspec) {
     while (!(rtcp->rtc->ISR & RTC_ISR_WUTWF))
       ;
     rtcp->rtc->WUTR = wakeupspec->wutr & 0xFFFF;
-    rtcp->rtc->CR   = (wakeupspec->wutr >> 16) & 0x7;
+    rtcp->rtc->CR &= ~RTC_CR_WUCKSEL;
+    rtcp->rtc->CR |= (wakeupspec->wutr >> 16) & RTC_CR_WUCKSEL;
     rtcp->rtc->CR |= RTC_CR_WUTIE;
     rtcp->rtc->CR |= RTC_CR_WUTE;
   }
diff --git a/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.h b/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.h
index e42b400e8..ad2807a0e 100644
--- a/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.h
+++ b/os/hal/ports/STM32/LLD/RTCv2/hal_rtc_lld.h
@@ -160,6 +160,7 @@ typedef struct {
   /**
    * @brief   Wakeup as encoded in RTC WUTR register.
    * @note    ((WUTR == 0) || (WUCKSEL == 3)) are a forbidden combination.
+   * @note    Bits 16..18 are copied in the CR bits 0..2 (WUCKSEL).
    */
   uint32_t                  wutr;
 } RTCWakeup;