Lightning-generated nitrogen oxides (LNO_x) greatly influence tropospheric photochemistry. The most common parameterisation of lightning flash rate used to calculate LNO_x in global composition models underestimates measurements over the ocean by a factor of 20–25. We formulate and validate an alternative parameterisation to remedy this problem. The new scheme causes an increase in the ozone burden by 8.5 % and the hydroxyl radical by 13 %, and these have implications for climate and air quality.