The invention relates to a measuring apparatus (20) for determining a measured value in a gas flow while taking into account cross-sensitivities of the measuring appliance due to at least one additional constituent in the gas flow that interferes with the measured value of the measured gas. The measuring apparatus has a device for dividing an original gas flow (26) to be measured into a first measured gas flow (38) and a second measured gas flow (39), a device for changing the content of measured gas in the second measured gas flow (39) by changing an influencing variable that influences the content of the measured gas, a sensor element (22) having a sensor for determining the measured value, an evaluating unit for evaluating the measured values, wherein the first measured gas flow (38) and the changed second measured gas flow (39) are alternately fed to the sensor element (22) in order to determine a first intermediate measured value in the first measured gas flow (38) and to determine an intermediate measured value in the second measured gas flow (39), and the evaluating unit calculates the final measured value on the basis of the two intermediate measurement results. The invention further relates to a corresponding method for determining a measured value in a gas flow.