This paper analyzes a two-country model of currency, banks and endogenous default to study whether impediments to credit market integration across jurisdictions impact the desirability of a currency union. We show that when those impediments induce a higher cost for banks to manage cross-border credit compared to domestic credit, welfare may not be maximal under a regime of currency union. But a banking union that would suppress hurdles to banking integration restores the optimality of that currency arrangement. The empirical and policy implications in terms of banking union are discussed.