diff --git a/Source/HBIOS/std.asm b/Source/HBIOS/std.asm
index c552b5a3..a40da2d4 100644
--- a/Source/HBIOS/std.asm
+++ b/Source/HBIOS/std.asm
@@ -28,6 +28,7 @@ TRUE		.EQU 	~FALSE
 USENONE		.EQU	0		; NO DEBUG
 USEXIO		.EQU	1		; BASIC SERIAL DRIVER
 USEMIO		.EQU	2		; MEMORY BUFFER DRIVER
+USEZ80OPT	.EQU	FALSE		; USE UNOFFICIAL OP CODES
 WBWDEBUG	.EQU	USENONE
 ;
 ; PRIMARY HARDWARE PLATFORMS