A familiar move that philosophers of sport make in the debate on the doping-issue is to reject from the start the argument that doping comes down to cheating. The claim that doping is cheating is often rebutted with the argument that doping is only cheating when one accepts that the use of doping is unjustified in itself. In this paper I want to argue that putting aside the cheating-argument in this way comes, first, too easy, because essential complexities of what (...) cheating is, are neglected. And, second, it comes too soon, because spelling the cheating argument out throws new light on the debate about matters of justifying the rules and criteria concerning doping. I will confine myself in this paper to the claim that it is in any case the institutional authorities that professional athletes cheat on. The relations with other parties that apparently can be claimed to be cheated upon also, such as other athletes in competition, are left out. The argument from cheating takes its starting point from a principle of fidelity, taken from Scanlon. By this principle the morally acceptable conduct of those taking part in a practice is grounded in the way reciprocal expectations are raised between parties to the practice. I apply this principle to the relation between athletes and institutional authorities in sport practices. This argument can take the cheating argument to a new level of seriousness, especially in the sense that the arguments treated here support a plea for democratization of the procedures and a larger role of the sportsmen and sportswomen themselves, or so I will defend. (shrink)