Authentication is one of the most fundamental services in cryptography and information security. Compared with the traditional authentication methods, group authentication allows a group of users to be authenticated at once rather than authenticating each of these users individually. Therefore, it is more desirable in the group oriented environment, such as multicast/conference communications. In this paper, we first demonstrate that a recent group authentication scheme by Chien (Security and Communication Networks, 2017) suffers some security flaws, i.e. an adversary in the asynchronous communication model can pretend to be a legitimate group member without being detected. We then use the Anonymous Veto Networks (AV-net) to patch Chien’s scheme, so that its security can be rigorously proved in a well-defined security model.