[Haskell-beginners] Different ByteStrings, what now?

Hello once again! My forays into Haskell are once again stopped by my weak Haskell Fu. I am working with ProtocolBuffers and so far everything worked fine, but now I have encountered a problem. I am trying to serialize a message that contains, among other things, a blob of binary data. My problem now is to get that binary data into the message. The message requires the data type Text.ProtocolBuffers.Header.ByteString, whereas my data is of the type Data.ByteString. How can I turn one into the other or get my data into the right format in te first place? I tried to find a function to solve this, but I couldn't find it in the ProtoBuff documentation. Thanks Raf