A process for controlling an internal combustion engine, in which an actual position of a reciprocating gas valve is detected by a position sensor, a positional deviation is calculated from the actual position and a zero position, a total length change of the reciprocating gas valve is calculated as a function of the temperature of the reciprocating gas valve, a valve clearance of the reciprocating gas valve is determined from the positional deviation and the total length change, and the further operation of the internal combustion engine is determined on the basis of the valve clearance.