This paper develops a simple macro-financial model with costly enforcement and capital requirements to study how financial frictions interact with macroprudential policy. When the enforcement constraint binds, the competitive equilibrium is inefficient: the planner prefers a positive spread between equity and deposit funding costs to deal with a deposits interest rate pecuniary externality derived from the financial friction, while markets force them to converge. We show that the constrained-efficient allocation can be implemented through either a subsidy on equity issuance or an equivalent tax on deposits, though both require strong informational assumptions. A countercyclical capital buffer offers a more practical alternative, and we show theoretically and numerically that it can replicate the planner’s allocation.