diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 8cd9e5b077b64fabf16817af8229008d1f3dd0ca..9377da1e97c087cf8f2b49cdb182d4606aaf177a 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -70,6 +70,8 @@ static void stm32_usart_config_reg_rs485(u32 *cr1, u32 *cr3, u32 delay_ADE,
 	*cr3 |= USART_CR3_DEM;
 	over8 = *cr1 & USART_CR1_OVER8;
 
+	*cr1 &= ~(USART_CR1_DEDT_MASK | USART_CR1_DEAT_MASK);
+
 	if (over8)
 		rs485_deat_dedt = delay_ADE * baud * 8;
 	else