Recently, lightweight RFID authentication protocol has been investigated extensively due to the awareness of practical requirements on individual privacy, robust system security and resource limitation of low-cost tags. Research studies have demonstrated major advancements in the direction of designing a secure access control mechanism for RFID system with resource-constrained tags. In 2008, Burmester and Medeiros developed an EPC Class 1 Generation 2 (EPC Gen2) compliant authentication protocol, called TRAP-3, to support tag anonymity, data confidentiality and forward security in which only primitive computation functions such as 32-bit pseudo random generator and simple exclusive-or operation are required. Nevertheless.. TRAP-3 is vulnerable to desynchronization attack. The secret key value, which is shared between the tag and the backend database, can be out of synchronization by just performing a series of challenge-response operations. To remedy this authentication flaw, in this study we develop a countermeasure mechanism and accordingly gain security enhancement for TRAP-3.