diff --git a/vlib/crypto/md5/md5.v b/vlib/crypto/md5/md5.v
index 7b233d840f..2bd9bc87d2 100644
--- a/vlib/crypto/md5/md5.v
+++ b/vlib/crypto/md5/md5.v
@@ -106,7 +106,7 @@ pub fn (d mut Digest) checksum() []byte {
 	// tmp := [1 + 63 + 8]byte{0x80}
     mut tmp := [byte(0)].repeat(1 + 63 + 8)
 	tmp[0] = 0x80
-	pad := (55 - int(d.len)) % 64 // calculate number of padding bytes
+	pad := int((55 - int(d.len)) % u64(64)) // calculate number of padding bytes
 	binary.little_endian_put_u64(mut tmp.right(1+pad), d.len<<u64(3)) // append length in bits
     d.write(tmp.left(1+pad+8))