Much of world trade is dominated by a small number of large firms. Market power becomes problematic for the estimation of gravity equations because many policy interventions also influence market shares and hence prices and the value of trade flows. This column proposes a method to correct the resulting inaccuracies in gravity equation estimation by adjusting trade flows for market power effects by subtracting a correction term that depends on the market share a firm or country has in the market in question. It finds membership in the euro area increases bilateral trade flows by around 48% before correcting for market power, and 58% after correction.