PCT No. PCT/DE97/02358 Sec. 371 Date Aug. 18, 1998 Sec. 102(e) Date Aug. 18, 1998 PCT Filed Oct. 15, 1997 PCT Pub. No. WO98/27408 PCT Pub. Date Jun. 25, 1998Device for measuring the mass of a flowing medium has a measuring element accommodated in a measurement fitting, wherein a flow rectifier with a grating is provided upstream of the measuring element. For simple manufacturing, assembly, and precise alignment of a grating in relation to a flow rectifier, the flow rectifier has detent elements that can elastically deform during installation of the grating in order to secure the grating to the flow rectifier in a detachable fashion. The device provided for measuring the mass of a flowing medium, in particular for measuring the flow of an intake air mass for internal combustion engines.