--- sys/crypto/siphash/siphash_test.c
+++ sys/crypto/siphash/siphash_test.c
@@ -118,7 +118,8 @@ SipHash24_TestVectors(void)
 
 		SipHash24_Init(&ctx);
 		SipHash_SetKey(&ctx, k);
-		SipHash_Update(&ctx, in, i);
+		if (i > 0)
+			SipHash_Update(&ctx, in, i);
 		SipHash_Final(out, &ctx);
 
 		if (memcmp(out, vectors[i], 8) != 0) {