Can Catholics serve as godparents at an Anglican infant's baptism?

My wife and I (both Catholic) have been asked to serve as godparents at our niece's baptism. The child's parents are fully aware of our strong commitment to the Catholic faith. I've received conflicting advice, and I wonder if anyone here can point to clear teaching on whether or not it is licit for us to serve as godparents at a baptism in an Anglican church.