diff --git a/components/net/freemodbus/port/portserial_m.c b/components/net/freemodbus/port/portserial_m.c
index eb50cf51d323ae4e86c1059a652b785e0b123d34..f68794a6176eb0957be06b58b9886c6ef3d1dd14 100644
--- a/components/net/freemodbus/port/portserial_m.c
+++ b/components/net/freemodbus/port/portserial_m.c
@@ -130,12 +130,16 @@ void vMBMasterPortSerialEnable(BOOL xRxEnable, BOOL xTxEnable)
         /* enable RX interrupt */
         serial->ops->control(serial, RT_DEVICE_CTRL_SET_INT, (void *)RT_DEVICE_FLAG_INT_RX);
         /* switch 485 to receive mode */
+#if defined(RT_MODBUS_MASTER_USE_CONTROL_PIN)
         rt_pin_write(MODBUS_MASTER_RT_CONTROL_PIN_INDEX, PIN_LOW);
+#endif
     }
     else
     {
         /* switch 485 to transmit mode */
+#if defined(RT_MODBUS_MASTER_USE_CONTROL_PIN)
         rt_pin_write(MODBUS_MASTER_RT_CONTROL_PIN_INDEX, PIN_HIGH);
+#endif
         /* disable RX interrupt */
         serial->ops->control(serial, RT_DEVICE_CTRL_CLR_INT, (void *)RT_DEVICE_FLAG_INT_RX);
     }