In this paper, we show that the BKS transformation coming from geometric quantization of the cotangent bundle of Riemannian compact symmetric spaces is not always unitary. We will use representation theory of compact Lie groups and Peter-Weyl theory to deduce a simple method to study the unitarity of the transformation. In particular, we show that for S-5 this transformation is not unitary. Additionally, we show that in the limit h -> 0 (where h is Planck's constant) asymptotic unitarity holds for all compact symmetric spaces. (C) 2019 Elsevier B.V. All rights reserved.