The precision of an intake manifold model for a supercharged internal combustion engine can be improved, wherein a first pressure value in the inlet tract (3) downstream of a throttle valve (6) and upstream of a compressor (7) and second pressure value (3) downstream of the compressor (7) are calculated by means of the intake manifold model. Furthermore, a first reference pressure and a second reference pressure are recorded by two pressure sensors (13, 14). It is determined whether the internal combustion engine (1) is operating in charging mode or not. The intake manifold model is then corrected on a difference between the first pressure value and the first reference value and a difference between the second pressure value and the second reference value depending on whether the operating mode is the charging mode or not.