diff --git a/sha1/sha1-asm.S b/sha1/sha1-asm.S
index 4d185f9..f479fcc 100644
--- a/sha1/sha1-asm.S
+++ b/sha1/sha1-asm.S
@@ -284,8 +284,8 @@ sha1_lastBlock:
 	pop r25
 	subi r21, 2
 	ldi r19, 64
-	sub r22, r19
-	sbc r23, r1
+	add r22, r19
+	adc r23, r1
 	rjmp sha1_lastBlock
 sha1_lastBlock_prolog:
 	/* allocate space on stack */