diff --git a/inc/cdc_acm_protocol.h b/inc/cdc_acm_protocol.h
index 729e200..ae620a9 100644
--- a/inc/cdc_acm_protocol.h
+++ b/inc/cdc_acm_protocol.h
@@ -87,6 +87,7 @@
 #define BUS_NONE            0
 #define BUS_IBMPC           1
 #define BUS_SHUGART         2
+/*#define BUS_APPLE2        3*/ /* reserved for Adafruit_Floppy */
 
 
 /*