Policy and path updates are common causes of network instability, leading to service disruptions or vulnerable intermediate states. In this letter, we propose the reverse update, an update scheme for software-defined networking that guarantees to preserve properties of flows during the transition time. We prove through a formal model that the proposal achieves consistent policy updates, in which in-transit packets are always handled in the next forwarding hops by the same or a more recent policy. The main contributions are: 1) a relaxation of the concept of per-packet-consistency in the data plane of software-defined networking; and 2) a policy update scheme, proved to be consistent and efficient. A software-defined networking simulator was developed and validated. The results of our simulations show that the proposed reverse update scheme is faster and has lower overhead than the current two-phase update proposed in the literature.