Multi-fuel internal combustion engine operation

A multi-cylinder internal combustion piston engine (10) comprises a first fuel feed system (20) and a second fuel feed system (30). The engine is operated by supplying a first fuel to at least one of the cylinders. During the operation, control parameters are acquired from the engine indicating the combustion process with the first fuel in said at least one of the cylinders. In case a difference between any of the acquired control parameters and their respective target values is exessive, the introduction of the first fuel is stopped to said cylinder, and the introduction of a second fuel to said cylinder is commenced, while in other cylinders fuel supply remains unchanged. During engine operation with the first fuel, the feed system (30) of the second fuel is maintained in a standby state to allow for quick transition to the second fuel.