diff --git a/os/hal/ports/STM32/LLD/USARTv1/hal_serial_lld.c b/os/hal/ports/STM32/LLD/USARTv1/hal_serial_lld.c
index 65697703a..68e707edd 100644
--- a/os/hal/ports/STM32/LLD/USARTv1/hal_serial_lld.c
+++ b/os/hal/ports/STM32/LLD/USARTv1/hal_serial_lld.c
@@ -108,9 +108,9 @@ static void usart_init(SerialDriver *sdp, const SerialConfig *config) {
 #else
   if (sdp->usart == USART1)
 #endif
-    fck = STM32_PCLK2 / config->speed;
+    fck = (STM32_PCLK2 + config->speed / 2) / config->speed;
   else
-    fck = STM32_PCLK1 / config->speed;
+    fck = (STM32_PCLK1 + config->speed / 2) / config->speed;
 
   /* Correcting USARTDIV when oversampling by 8 instead of 16.
      Fraction is still 4 bits wide, but only lower 3 bits used.