diff --git a/Source/HBIOS/dbgmon.asm b/Source/HBIOS/dbgmon.asm
index a2a0ceac..69736962 100644
--- a/Source/HBIOS/dbgmon.asm
+++ b/Source/HBIOS/dbgmon.asm
@@ -960,7 +960,7 @@ ISHEX1:
 	JR	C,ISHEX2		; YES, NOT A-F, FAIL
 	CP	'F' + 1			; > 'F'
 	JR	NC,ISHEX2		; YES, NOT A-F, FAIL
-	XOR	A			; MUST BE 0-9, SET ZF
+	XOR	A			; MUST BE A-F, SET ZF
 	RET				; AND DONE
 ISHEX2:
 	OR	$FF			; CLEAR ZF