A grating for the formation of a reverse flow of a turbofan engine and comprising fins of a first type having a curved profile whose rounding is oriented aft and whose center of curvature is forward relative to the fin of the first type, fins of a second type having a curved profile whose rounding is oriented aft and whose center of curvature is forward relative to the fin of the second type. In this grating, each fin of one of the two types is inserted between two fins of the other type moving from forward to aft and the cord of the fins of the second type is smaller than the cord of the fins of the first type.