We give new and simpler proof for the undecidability of the n-permutation Post Correspondence Problem that was originally proved by K. Ruohonen [10]. Our proof uses a recent result on deterministic semi-Thue systems according to which it is undecidable for a given deterministic semi-Thue system T and a word u whether or not there exists a nonempty cyclic derivation is u in u -> (+)(T) u. (C) 2015 Elsevier B.V. All rights reserved.