In a closed-loop scenario, the performance of transmit-diversity schemes for a multiple antenna system depends on the reliability of the channel state information (CSI). However, estimating the reliability of the instantaneous CSI at the transmitter is a challenging task. In this paper, we propose a robust transmit-diversity scheme for the case when the instantaneous CSI available at the transmitter is imperfect and its reliability is unknown to the transmitter. We show by simulation that our proposed scheme is efficient when the CSI reliability varies arbitrarily in every channel realization.