diff --git a/kernel/parse.asm b/kernel/parse.asm
index 3935e31..ca2eca9 100644
--- a/kernel/parse.asm
+++ b/kernel/parse.asm
@@ -11,16 +11,26 @@
 ; On success, the carry flag is reset. On error, it is set.
 parseHex:
 	; First, let's see if we have an easy 0-9 case
-	
-	add 	a, 0xc6	; maps '0'-'9' onto 0xf6-0xff
-	sub 	0xf6	; maps to 0-9 and carries if not a digit
-	ret	nc
+	cp	'0'
+	jr	c, .error	; if < '0', we have a problem
+	cp	'9'+1
+	jr	nc, .alpha	; if >= '9'+1, we might have alpha
+	; We are in the 0-9 range
+	sub	'0'		; C is clear
+	ret
 
-	and 	0xdf		; converts lowercase to uppercase
-	add	a, 0xe9		; map 0x11-x017 onto 0xFA - 0xFF
-	sub 	0xfa		; map onto 0-6
-	ret 	c
-	add	a, 10		; C is clear, map back to 0xA-0xF
+.alpha:
+	call	upcase
+	cp	'A'
+	jr	c, .error	; if < 'A', we have a problem
+	cp	'F'+1
+	jr	nc, .error	; if >= 'F', we have a problem
+	; We have alpha.
+	sub	'A'-10		; C is clear
+	ret
+
+.error:
+	scf
 	ret
 
 ; Parses 2 characters of the string pointed to by HL and returns the numerical