According to the dogmatist, knowing p makes it rational to disregard future evidence against p. The standard response to the dogmatist holds that knowledge is defeasible: acquiring evidence against something you know undermines your knowledge. However, this response leaves a residual puzzle, according to which knowledge makes it rational to intend to disregard future counterevidence. I argue that we can resolve this residual puzzle by turning to an unlikely source: Kavka’s toxin puzzle. One lesson of the toxin puzzle is that it is irrational to intend to do that which you know will be irrational. This yields a simple reply to the dogmatist: it is irrational to intend to disregard future evidence because you can know in advance that it will be irrational to do so.