Radio frequency identification systems which use radio frequency for object identification are widely developed nowadays. Security problems such as privacy and untraceability had lead to propose numerous protocols for RFID systems. However most of these attempts have not been successful.In this paper we present a desynchronization attack against a recently proposed RFID protocol called Anonymous Forward-Secure Mutual Authentication or in short AFMAP. The complexity of attack is a few runs of the protocol and the success probability is 1. To the best of our knowledge, this is the first attack on AFMAP.