In constitutional political economy, the citizens' constitutional interests determine the social contract that is binding for the post-constitutional market game. However, following traditional preference subjectivism, it is left open what the constitutional interest are. Using the example of risk attitudes, we argue that this approach is too parsimonious with regard to the behavioral foundations to support a calculus of consent. In face of innovative activities with pecuniary and technological externalities in the post-constitutional phase, the citizens' constitutional interests vary with their risk preferences. To determine what kind of social contract is generally agreeable, specific assumptions about risk preferences are needed.