./validate --testsuite-only not working

Not sure if I'm doing something wrong, but looking at the validate script, $thisdir and $ghc are only set if --testsuite-only is not passed, which causes $testghc to be set to /, which gets me this command (Note the value of --test-compiler):

.../hadrian/dist-newstyle/build/x86_64-osx/ghc-8.8.3/hadrian-0.1.0.0/x/hadrian/build/hadrian/hadrian -j13 --build-root=_validatebuild -V test --test-speed=normal               --test-compiler="/"               --summary=/testsuite_summary.txt               --summary-junit=/testsuite.xml

And this error:

# test
# _validatebuild/test/ghcconfig
_validatebuild/test/bin/ghc-config /
ghc-config: /: readCreateProcess: runInteractiveProcess: exec: permission denied (Permission denied)
Error when running Shake build system:
  at want, called at src/Main.hs:100:30 in main:Main
* Depends on: test
  at need, called at src/Rules/Test.hs:107:9 in main:Rules.Test
* Depends on: _validatebuild/test/ghcconfig
  at cmd, called at src/Rules/Test.hs:97:9 in main:Rules.Test
* Raised the exception:
Development.Shake.cmd, system command failed
Command line: _validatebuild/test/bin/ghc-config /
Exit code: 1
Stderr:
ghc-config: /: readCreateProcess: runInteractiveProcess: exec: permission denied (Permission denied)