diff --git a/src/main/drivers/serial_uart_stm32f4xx.c b/src/main/drivers/serial_uart_stm32f4xx.c
index 2f72317ea..79d3e18ad 100644
--- a/src/main/drivers/serial_uart_stm32f4xx.c
+++ b/src/main/drivers/serial_uart_stm32f4xx.c
@@ -345,12 +345,12 @@ uartPort_t *serialUART(UARTDevice device, uint32_t baudRate, portMode_t mode, po
     else {
         if (mode & MODE_TX) {
             IOInit(tx, OWNER_SERIAL_TX, RESOURCE_INDEX(device));
-            IOConfigGPIOAF(tx, IOCFG_AF_PP, uart->af);
+            IOConfigGPIOAF(tx, IOCFG_AF_PP_UP, uart->af);
         }
 
         if (mode & MODE_RX) {
             IOInit(rx, OWNER_SERIAL_RX, RESOURCE_INDEX(device));
-            IOConfigGPIOAF(rx, IOCFG_AF_PP, uart->af);
+            IOConfigGPIOAF(rx, IOCFG_AF_PP_UP, uart->af);
         }
     }