diff --git a/targets/TARGET_STM/serial_api.c b/targets/TARGET_STM/serial_api.c
index c805669..b7ce63f 100644
--- a/targets/TARGET_STM/serial_api.c
+++ b/targets/TARGET_STM/serial_api.c
@@ -629,8 +629,12 @@
 #if defined(UART_ONE_BIT_SAMPLE_DISABLE) // F0/F3/F7/G0/H7/L0/L4/L5/WB
     huart->Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
 #endif
-#if defined(UART_PRESCALER_DIV1) // G0/H7/L4/L5/WB
-    huart->Init.ClockPrescaler = UART_PRESCALER_DIV1;
+#if defined(UART_PRESCALER_DIV1) // G0/G4/H7/L4/L5/U5/WB/WL
+    if (obj_s->baudrate < 4800) {
+        huart->Init.ClockPrescaler = UART_PRESCALER_DIV16;
+    } else {
+        huart->Init.ClockPrescaler = UART_PRESCALER_DIV1;
+    }
 #endif
 #if defined(UART_ADVFEATURE_NO_INIT) // F0/F3/F7/G0/H7/L0/L4//5/WB
     huart->AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;