Monetary economists have long recognized a tension between the benefits of fractional reserve banking, such as the ability to undertake more profitable (long‐term) investment opportunities, and the difficulties associated with it, such as the risk of insolvency for each bank and the associated losses to bank liability holders. I show that a specific banking arrangement (a joint‐liability scheme) provides an effective mechanism for ensuring the ex post transfer of reserves from liquid banks to illiquid banks, so it is possible to select a socially efficient reserve ratio in the banking system that preserves the safety of bank liabilities as a store of value and maximizes the rate of return paid to bank liability holders.