Concerns about the procyclicality of bank regulation have motivated recent reforms that include countercyclical measures. This paper analyzes how optimal capital requirements, which balance a trade-off between financial stability and investment of the real sector, adjust during a downturn. Adding an endogenous loan market reveals equilibrium effects that strongly influence the adjustment and allows studying the implications of real shocks. The results suggest a nuanced adjustment depending on the shock: In a capital crunch, capital requirements are relaxed to prevent a sharp decline in investment. If productivity decreases, they are tightened as preserving financial stability entails a smaller cost.