Thanks for all the work you've been doing on the Windows build. As requested by Tamar I removed ghc-tarballs, and reconfigured. Then I built from scratch. I get the following testsuite failures Simon Unexpected failures: ghci/prog003/prog003.run prog003 [bad exit code] (ghci) plugins/plugins05.run plugins05 [exit code non-0] (normal) plugins/plugins01.run plugins01 [bad exit code] (normal) plugins/plugins07.run plugins07 [bad exit code] (normal) plugins/T10420.run T10420 [bad exit code] (normal) plugins/T10294a.run T10294a [bad exit code] (normal) plugins/T11244.run T11244 [bad stderr] (normal) plugins/T12567a.run T12567a [bad exit code] (normal) rts/testmblockalloc.run testmblockalloc [bad exit code] (normal) simplCore/should_compile/T7702.run T7702 [exit code non-0] (normal) Unexpected stat failures: perf/haddock/haddock.compiler.run haddock.compiler [stat not good enough] (normal) Framework failures: ghci/scripts/ghci062.run ghci062 [ghci-ext] ([Errno 17] File exists: '/c/Users/simonpj/AppData/Local/Temp/ghctest-anc5s5mh/test spaces/./ghci/scripts/ghci062.run') plugins/plugins07.run plugins07 [normal] (pre_cmd failed: 2) plugins/T10420.run T10420 [normal] (pre_cmd failed: 2) plugins/T10294a.run T10294a [normal] (pre_cmd failed: 2) plugins/T11244.run T11244 [normal] (pre_cmd failed: 2) th/TH_repPrim.run TH_repPrim [ext-interp] ([Errno 17] File exists: '/c/Users/simonpj/AppData/Local/Temp/ghctest-anc5s5mh/test spaces/./th/TH_repPrim.run') th/TH_repPatSig.run TH_repPatSig [ext-interp] ([Errno 17] File exists: '/c/Users/simonpj/AppData/Local/Temp/ghctest-anc5s5mh/test spaces/./th/TH_repPatSig.run')