More pain. I said sh validate --fast --no-clean and got this output Error when running Shake build system: at action, called at src/Rules.hs:71:19 in main:Rules at need, called at src/Rules.hs:93:5 in main:Rules * Depends on: _validatebuild/stage1/lib/package.conf.d/base-4.14.0.0.conf at need, called at src/Rules/Register.hs:113:5 in main:Rules.Register * Depends on: _validatebuild/stage1/libraries/base/build/libHSbase-4.14.0.0-ghc8.11.0.20191201.so at need, called at src/Rules/Library.hs:146:5 in main:Rules.Library * Depends on: _validatebuild/stage1/libraries/base/build/GHC/IO/Handle/Lock/Common.dyn_o at &%>, called at src/Rules/Compile.hs:54:7 in main:Rules.Compile * Depends on: _validatebuild/stage1/libraries/base/build/GHC/IO/Handle/Lock/Common.dyn_o _validatebuild/stage1/libraries/base/build/GHC/IO/Handle/Lock/Common.dyn_hi at error, called at src/Development/Shake/Internal/Rules/Files.hs:245:13 in shake-0.18.3-593067565aafb558d09b4352b8abc327d8911a39a0e9abab2804b002b1ae536e:Development.Shake.Internal.Rules.Files * Raised the exception: Error, &%> rule failed to produce 1 file (out of 2) _validatebuild/stage1/libraries/base/build/GHC/IO/Handle/Lock/Common.dyn_o _validatebuild/stage1/libraries/base/build/GHC/IO/Handle/Lock/Common.dyn_hi - MISSING I think I'm going to have to revert to 'sh validate -legacy'. Please let me know when I should try again with Hadrian. Simon