Thanks for the help but I think that's not the issue because (get-lib-search-dirs) returns exactly the same thing on a machine where this is working perfectly as on the machine where it isn't. The machine where it is not working is a virtual machine with a stock install of macOS High Sierra and a relatively fresh install of Racket. This VM is meant for development and testing. This particular clone of the reference VM has been used for a little while but it should still be close to the reference. So, on the one hand, it's surprising that this is happening here, with something so close to stock configuration. On the other hand, the machine where it is working has been beaten into submission to run all kinds of development tools over a period of years.