We investigate the effects from the introduction of a closing call auction (CCA) at the index futures market. Limit order book models, where trader patience determines trading strategies, predict that a CCA increases trader patience and, hence, improves closing price accuracy and end‐of‐day liquidity. We find that the introduction leads to increased trader patience, improved futures closing price accuracy, unaffected tightness and resiliency, and decreased depth. Decreased depth is likely due to less order fishing activity. With the CCA, opportunistic patient traders' posting of limit orders deep in the order book, to profit from impatient traders, is no longer feasible.