Computer and telecommunications advances in the last years allowed new distributed applications developments. In this context, time synchronization is a very important issue. Many industrial sectors, such as financial and power, need to achieve high time accuracy. The IEEE 1588–2008 standard [1] defines the second version of PTP, designed to archive clock accuracy in the sub-microsecond range. Previous works [2] [3] has shown PTP vulnerability to byzantine failures. This paper describes an alternative to improve PTP robustness to the byzantine failure without modifying PTP slaves.