diff --git a/os/hal/ports/STM32/LLD/RTCv1/hal_rtc_lld.c b/os/hal/ports/STM32/LLD/RTCv1/hal_rtc_lld.c
index 86752d3e5..248a9c3cc 100644
--- a/os/hal/ports/STM32/LLD/RTCv1/hal_rtc_lld.c
+++ b/os/hal/ports/STM32/LLD/RTCv1/hal_rtc_lld.c
@@ -130,7 +130,7 @@ static void rtc_decode(uint32_t tv_sec,
                        RTCDateTime *timespec) {
   struct tm tim;
   struct tm *t;
-  const time_t time = tv_sec; /* Copy with implicit type conversion.*/
+  const time_t time = (const time_t)tv_sec;   /* Could be 64 bits.*/
 
   /* If the conversion is successful the function returns a pointer
      to the object the result was written into.*/