AbstractIn her inventive and tightly argued book Defensive Killing, Helen Frowe defends the view that bystanders—those who do not pose threats to others—cannot be liable to being harmed in self-defence or in defence of others. On her account, harming bystanders always infringes their rights against being harmed, since they have not acted in any way to forfeit them. According to Frowe, harming bystanders can be justified only when it constitutes a lesser evil. In this brief essay, I make the case that some bystanders can indeed be liable to harm. They can be liable, I will argue, because they can be morally responsible for threats of harm, and in becoming responsible they can forfeit their rights. While bystanders cannot be responsible for initiating threats, they can become responsible for the persistence of threats, and for culpably failing to prevent them from being initiated in the first place.