Neo-Kantian accounts which try to ground morality in the necessary requirements of agency face the problem of "bad action". The most prominent example is Christine Korsgaard's version of constitutivism that considers the categorical imperative to be indispensable for an agent's self-constitution. In my paper I will argue that a constitutive account can solve the problem of bad action by applying the distinction between constitutive and regulative rules to the categorical imperative. The result is that an autonomous agent can violate the categorical imperative in so far as it amounts to a regulative rule of morality; however, an agent cannot call into question the categorical imperative as a constitutive rule of the practice of morality without losing her or his identity as a moral agent. The paper then compares this approach to bad action with the one Korsgaard provides and outlines also a new way of grounding the categorical imperative.