The invention relates to balancing the cylinders of an internal combustion engine. The invention comprises cylinder-specific pressure sensors (1) installed in the cylinders of an internal combustion engine for measuring the cylinder pressures as well as an adjustment unit (2). The adjustment unit is arranged to determine the maximum pressure and knock value of each cylinder as well as the mean maximum pressure of the cylinders as a response to the measurements of cylinder pressures and to determine the differences between the maximum pressure of each cylinder and the mean maximum pressure. The differences are compared to a certain deviation range of the mean maximum pressure and the knock value to a certain knock limit value. The duration of the fuel injection of the cylinder is adjusted in case the difference of a single cylinder exceeds the lower limit of the deviation range and the knock value of the cylinder is less than the knock limit value or the difference of the cylinders exceeds the upper limit of the deviation range.