@jcfr I just noticed that it’s still not working. See http://slicer.cdash.org/viewConfigure.php?buildid=1202036
For any reason, PETDICOMExtension[1,2] cannot be found by CMake.
[1] https://github.com/Slicer/ExtensionsIndex/blob/master/PETDICOMExtension.s4ext#L9-L10
[2] https://github.com/QIICR/Slicer-PETDICOMExtension/blob/master/CMakeLists.txt#L34-L35