A device for determining at least one parameter of a medium flowing in a line, in particular for determining the air mass flow rate in the intake manifold of an internal combustion engine, which include a line component 3 and a sensor device 1 having a bypass part 6, are known. To prevent separation of the flow at the sidewalls of the bypass part, it is provided that a flow diversion element 2 be positioned in the line component 3 upstream from the bypass part 6 with respect to the main flow direction 18 and have at least one diversion surface 20 facing the main flow direction 18, which, starting from an apex line 25 located at a distance from the bypass part 6, curves evenly on both sides toward the two sidewalls 16, 17 so that the ends 38 of the diversion surface 20 facing away from the apex line are aligned with the sidewalls 16, 17.