This document specifies a multicast handover optimization mechanism for Proxy Mobile IPv6 to accelerate the delivery of multicast traffic to mobile nodes after handovers. The mechanism is based on speeding up the acquisition of mobile nodes' multicast context by the mobile access gateways. To do that, extensions to the current Proxy Mobile IPv6 protocol are proposed. These extensions are not only applicable to the base solution for multicast support in Proxy Mobile IPv6, but they can also be applied to other solutions being developed to avoid the tunnel convergence problem. Furthermore, they are also independent of the role played by the mobile access gateway within the multicast network (either acting as multicast listener discovery proxy or multicast router).