diff --git a/Source/HBIOS/plt_mk4.inc b/Source/HBIOS/plt_mk4.inc
index ce4d0f79..7e921886 100644
--- a/Source/HBIOS/plt_mk4.inc
+++ b/Source/HBIOS/plt_mk4.inc
@@ -13,4 +13,8 @@ MK4_RTC		.EQU	MK4_BASE + $0A	; RTC INTERFACE REGISTER
 RTC		.EQU	MK4_RTC		; GENERIC ALIAS FOR RTC PORT
 ;
 Z180_BASE	.EQU	$40		; I/O BASE ADDRESS FOR INTERNAL Z180 REGISTERS
+;
+;
+FIFO_BASE       .EQU	$0C		; ECB USB-FIFO DEFAULT PORT
+;
 #INCLUDE "z180.inc"