The issue is how CMake decides to order "include_directories". There are (if I recall correctly) 4 primary sources of these via properties: for the directory, for individual sources, for to-be-built targets, and for linkage targets. The ordering of these is critical, since our goal is to list in-tree headers/linkage before out-of-tree headers/linkage. I'd have to go back to my work to remember how CMake orders these, but what I do recall is that the last one (for linkage targets) doesn't come last, which seems wrong to me: any out-of-tree property should always come last in any ordering! And, I could not figure out an easy or clean way to force the ordering to work for our goal. It's an unfortunate confluence of moving to "modern CMake" linkage targets and how CMake works internally. Once I'm caught up with UHD, GR, and Volk backlog from being away for 2 weeks, I'll look into this issue again since it's pretty critical for MacPorts that this work! Hope this is useful and maybe makes some sense! - MLD