A combine harvester with a separator for separating a flow of harvested material into a material fraction and a residual material flow, a spreader extending in a width direction for ejecting the residual material flow from the combine harvester, wherein a dividing line running transverse to the width direction defines a first region of the spreader through which a first portion of the residual material flow is passed, and a second region of the spreader through which a second portion of the residual material flow is passed, a material guiding element disposed at an outlet from the separator and which can be adjusted between positions which respectively bring about different distributions in the width direction of the residual material flow entering the spreader, sensors distributed in the width direction, each of which being configured to detect the size of a fraction of the residual material flow passing in the vicinity of the sensor and for delivering an output signal which is representative of the size of the fraction, wherein a first group of the sensors is disposed in the first region of the spreader and a second group of the sensors is disposed in the second region and at least the first group comprises a plurality of sensors, and a control unit for controlling the position of the material guiding element, wherein the control unit is configured to generate a signal which is proportional to the size of the fraction of the residual material flow from each output signal from a sensor, for adding the proportional signals from the sensors of at least the first group in order to obtain signals which are proportional to the size of the first and of the second portions of the residual material flow, for comparing the ratio of the signals which are proportional to the first and second portion with a nominal ratio and for adjusting the material guiding element in the event of a discrepancy between the ratio of the signals which are proportional to the first and second portion and the nominal ratio. a separator for separating a flow of harvested material into a material fraction and a residual material flow, a spreader extending in a width direction for ejecting the residual material flow from the combine harvester, wherein a dividing line running transverse to the width direction defines a first region of the spreader through which a first portion of the residual material flow is passed, and a second region of the spreader through which a second portion of the residual material flow is passed, a material guiding element disposed at an outlet from the separator and which can be adjusted between positions which respectively bring about different distributions in the width direction of the residual material flow entering the spreader, sensors distributed in the width direction, each of which being configured to detect the size of a fraction of the residual material flow passing in the vicinity of the sensor and for delivering an output signal which is representative of the size of the fraction, wherein a first group of the sensors is disposed in the first region of the spreader and a second group of the sensors is disposed in the second region and at least the first group comprises a plurality of sensors, and a control unit for controlling the position of the material guiding element, wherein the control unit is configured to generate a signal which is proportional to the size of the fraction of the residual material flow from each output signal from a sensor, for adding the proportional signals from the sensors of at least the first group in order to obtain signals which are proportional to the size of the first and of the second portions of the residual material flow, for comparing the ratio of the signals which are proportional to the first and second portion with a nominal ratio and for adjusting the material guiding element in the event of a discrepancy between the ratio of the signals which are proportional to the first and second portion and the nominal ratio.