The invention relates to a device for protecting (24) a gas engine (12), especially a stationary gas engine, for regulating at least one parameter (Pj) of the engine (12), said device comprising means (26) for obtaining an index (IMi; IMg) which represents the combustion behaviour of a gas to be potentially supplied to the engine (12). The invention is characterised in that the device also comprises means (28) for determining an optimum regulating value of the parameter in view of the index obtained (IMi; IMg).