Method for controlling an internal combustion engine

A method for controlling an internal combustion engine (100) supplied with gaseous fuel of a varying gas composition is disclosed. The method comprises receiving (step 504) a knock data (400) corresponding to knock levels (402) over a time period of a varying gas composition, determining (point 506A) from the knock data (400) that the knock levels (402) have a tendency (403A, 403B, 403C) to change over the time period, and accordingly that a variation in the gas composition of the gaseous fuel supplied to the internal combustion engine has occurred, and adjusting (step 510) an operating condition of the internal combustion engine to adapt a knock susceptibility of the internal combustion engine (100) to the varying gas composition.