When trying to prove the security of a protocol, one usually analyzes the protocol in isolation, i.e., in a network with no other protocols. But in reality, there will be many protocols operating on the same network, maybe even sharing data including keys, and an intruder may use messages of one protocol to break another. We call that a multi-protocol attack. In this paper, we try to find such attacks using the Tamarin prover. We analyze both examples that were previously analyzed by hand or using other tools, and find novel attacks.