Re-platforming - the transfer of a legacy system to a new target platform - is often seen as a first cost-reduction step to enable a long term reengineering effort of a legacy system. However, recreating a functionally equivalent ecosystem on a different platform entails significant technical and organisational challenges. This extended abstract describes challenges, their solutions as well as an important lesson learned during a re-platforming project of 40 year old PL/I and COBOL applications.