diff --git a/src/main/drivers/io.h b/src/main/drivers/io.h
index 61905cc54..d45f8b91b 100644
--- a/src/main/drivers/io.h
+++ b/src/main/drivers/io.h
@@ -66,6 +66,7 @@
 #define IOCFG_AF_PP_PD       IO_CONFIG(GPIO_Mode_AF,  0, GPIO_OType_PP, GPIO_PuPd_DOWN)
 #define IOCFG_AF_PP_UP       IO_CONFIG(GPIO_Mode_AF,  0, GPIO_OType_PP, GPIO_PuPd_UP)
 #define IOCFG_AF_OD          IO_CONFIG(GPIO_Mode_AF,  0, GPIO_OType_OD, GPIO_PuPd_NOPULL)
+#define IOCFG_AF_OD_UP       IO_CONFIG(GPIO_Mode_AF,  0, GPIO_OType_OD, GPIO_PuPd_UP)
 #define IOCFG_IPD            IO_CONFIG(GPIO_Mode_IN,  0, 0,             GPIO_PuPd_DOWN)
 #define IOCFG_IPU            IO_CONFIG(GPIO_Mode_IN,  0, 0,             GPIO_PuPd_UP)
 #define IOCFG_IN_FLOATING    IO_CONFIG(GPIO_Mode_IN,  0, 0,             GPIO_PuPd_NOPULL)
diff --git a/src/main/drivers/serial_uart_stm32f4xx.c b/src/main/drivers/serial_uart_stm32f4xx.c
index 0f1dc8dbb..f00fbfce6 100644
--- a/src/main/drivers/serial_uart_stm32f4xx.c
+++ b/src/main/drivers/serial_uart_stm32f4xx.c
@@ -281,7 +281,7 @@ uartPort_t *serialUART(UARTDevice_e device, uint32_t baudRate, portMode_e mode,
 
     if (options & SERIAL_BIDIR) {
         IOInit(txIO, OWNER_SERIAL_TX, RESOURCE_INDEX(device));
-        IOConfigGPIOAF(txIO, ((options & SERIAL_BIDIR_PP) || (options & SERIAL_BIDIR_PP_PD)) ? IOCFG_AF_PP : IOCFG_AF_OD, hardware->af);
+        IOConfigGPIOAF(txIO, ((options & SERIAL_BIDIR_PP) || (options & SERIAL_BIDIR_PP_PD)) ? IOCFG_AF_PP : IOCFG_AF_OD_UP, hardware->af);
     } else {
         if ((mode & MODE_TX) && txIO) {
             IOInit(txIO, OWNER_SERIAL_TX, RESOURCE_INDEX(device));