diff --git a/usb_serial.c b/usb_serial.c
index d10cb9f..84ad021 100644
--- a/usb_serial.c
+++ b/usb_serial.c
@@ -31,6 +31,9 @@
 // Version 1.7: fix usb_serial_set_control
 // 2012-10-17: Import to Teacup firmware
 
+/* protect this file from Arduino IDE */
+#ifdef USE_USB
+
 #define USB_SERIAL_PRIVATE_INCLUDE
 #include "usb_serial.h"
 
@@ -934,4 +937,4 @@ ISR(USB_COM_vect)
 	UECONX = (1<<STALLRQ) | (1<<EPEN);	// stall
 }
 
-
+#endif /* USE_USB */