diff --git a/stm32/usb/usb_device.c b/stm32/usb/usb_device.c
index 6ba479d..d02af42 100755
--- a/stm32/usb/usb_device.c
+++ b/stm32/usb/usb_device.c
@@ -34,6 +34,8 @@
 /* USER CODE BEGIN PV */
 /* Private variables ---------------------------------------------------------*/
 
+FILE *vcp_usb;
+
 /* USER CODE END PV */
 
 /* USER CODE BEGIN PFP */
diff --git a/stm32/usb/usbd_cdc_if.h b/stm32/usb/usbd_cdc_if.h
index b46f64e..9e14977 100755
--- a/stm32/usb/usbd_cdc_if.h
+++ b/stm32/usb/usbd_cdc_if.h
@@ -116,7 +116,7 @@ extern uint16_t CDC_RX_LEN;
 uint8_t CDC_Transmit_FS(uint8_t* Buf, uint16_t Len);
 
 /* USER CODE BEGIN EXPORTED_FUNCTIONS */
-FILE *vcp_usb;
+extern FILE *vcp_usb;
 int usb_write(void *cookie, const char *buf, int len);
 #define usb_printf(...)	fprintf(vcp_usb, __VA_ARGS__)
 uint16_t vcp_status(void);