Abstract-Many location-based services for alerting persons of nearby friends have been deployed in practice. A drawback of most approaches to providing such services is that friends always learn each other's location even when they are not actually nearby. The Louis protocol proposed by Zhong, Goldberg and Hengartner aims to ensure that a friend's location is revealed to another friend if and only if the friends are actually nearby. The protocol lets a third party learn whether the friends are nearby, without the third party learning their location. The third party communicates the answer to the person who invokes the service. A key feature of the protocol is that a person can detect misbehavior by the third party or the person's friend. This paper reveals a flaw in the way the protocol handles the detection of the misbehaving party, leading to an unauthorized disclosure of a person's location. Two alternatives for fixing the flaw in the protocol are proposed and a heuristic analysis is given.