A device for compacting fiber flocks into a flock mat has means for supplying the fiber flocks, a discharge belt for carrying the compacted flock mat away, and walls, which are arranged opposite each other between the means for supplying the fiber flocks and the discharge belt and thus form the boundaries of an essentially vertical chute feed, which defines the transport direction of the fiber flocks. At least one of the walls is supported in such a way that its movement during each cycle has a component in the transport direction of the fiber flocks and a component in the direction transverse to the transport direction.