diff --git a/src/convert.asm b/src/convert.asm
index 095515a..87ad7b2 100644
--- a/src/convert.asm
+++ b/src/convert.asm
@@ -130,8 +130,8 @@ hex2str:
 		div	r8
 		cmp	rdx, 10
 		jb	.num
-		cmp	r9, 0
-		je	.lower
+		test	r9, r9
+		jz	.lower
 		;.upper:
 		add	rdx, 55
 		jmp	.push