This article assesses the moral importance of a humanitarian intervener's fidelity to the principles of international humanitarian law or jus in bello (principles of just conduct in war). I begin by outlining the particular principles of jus in bello that an intervener should follow when discharging the responsibility to protect, drawing on Jeff McMahan's recent work. The second section considers more broadly the moral underpinnings of these principles. I claim that consequentialist justifications of these principles cannot fully grasp their moral significance and, in particular, the difference between doing and allowing. Overall, I argue that these principles are (i) more important and (ii) more stringent in the context of humanitarian intervention.