diff --git a/components/net/freemodbus/port/portserial_m.c b/components/net/freemodbus/port/portserial_m.c
index 366dc799835e0759bd02e2477bf39c3453dfbc5e..eb50cf51d323ae4e86c1059a652b785e0b123d34 100644
--- a/components/net/freemodbus/port/portserial_m.c
+++ b/components/net/freemodbus/port/portserial_m.c
@@ -57,7 +57,9 @@ BOOL xMBMasterPortSerialInit(UCHAR ucPORT, ULONG ulBaudRate, UCHAR ucDataBits,
      * set 485 mode receive and transmit control IO
      * @note MODBUS_MASTER_RT_CONTROL_PIN_INDEX need be defined by user
      */
+#if defined(RT_MODBUS_MASTER_USE_CONTROL_PIN)
     rt_pin_mode(MODBUS_MASTER_RT_CONTROL_PIN_INDEX, PIN_MODE_OUTPUT);
+#endif
 
     /* set serial name */
     if (ucPORT == 1) {