Friends I'm getting this from my newly-built in-tree compiler ~/code/HEAD-11/_build/ghc-stage1 -c T24984.hs -O T24984.hs:1:1: error: [ ]8;;https://errors.haskell.org/messages/GHC-45102 \GHC-45102 ]8;; \] Ambiguous module name ‘Prelude’. * it was found in multiple packages: base-4.22.0.0 base-4.22.0.0* What a bonkers message. What is going wrong? I do see this: ls -d /home/simonpj/code/HEAD-11/_build/stage1/lib/x86_64-linux-ghc-9.15.20251119/base* /home/simonpj/code/HEAD-11/_build/stage1/lib/x86_64-linux-ghc-9.15.20251119/base-4.22.0.0-c7d2 /home/simonpj/code/HEAD-11/_build/stage1/lib/x86_64-linux-ghc-9.15.20251119/base-4.22.0.0-inplace simonpj@LHR-WD-22561:~/code/HEAD-11/testsuite/tests/perf/compiler$ So there are two base packages around somehow. I don't know if that's the reason. I'd love a bit of help.. it's super annoying Maybe it's some leftover not-clean stuff -- but how would I diagnose? How can I see what package directories it is looking in, which package files it is reading? THanks Simon