Decoding the last bytes of a stream?

I am making a dissector that calculates the remaining length of a stream, and decodes it in as many groups of 11 bytes as possible. However, whenever it decodes the last couple of bytes I get an error saying malformed packets.

This does not happen when the last possible 11 byte group ends and there are 6 or so bytes left over.

The packets that I am testing this on I had created using a custom packet building program. So I'm wondering if this malformed packet message is due to me creating bad packets or if you are just unable to decode the last couple bits in a stream.