This has started happening when I do 'sh validate -no-clean' "inplace/bin/ghc-cabal" configure libraries/ghc-prim dist-install --with-ghc="/home/simonpj/5builds/HEAD-5/inplace/bin/ghc-stage1" --with-ghc-pkg="/home/simonpj/5builds/HEAD-5/inplace/bin/ghc-pkg" --disable-library-for-ghci --enable-library-vanilla --enable-library-for-ghci --disable-library-profiling --enable-shared --with-hscolour="/home/simonpj/.cabal/bin/HsColour" --configure-option=CFLAGS="-Wall -fno-stack-protector -Werror=unused-but-set-variable -Wno-error=inline" --configure-option=LDFLAGS=" " --configure-option=CPPFLAGS=" " --gcc-options="-Wall -fno-stack-protector -Werror=unused-but-set-variable -Wno-error=inline " --with-gcc="gcc" --with-ld="ld.gold" --with-ar="ar" --with-alex="/home/simonpj/.cabal/bin/alex" --with-happy="/home/simonpj/.cabal/bin/happy" Configuring ghc-prim-0.5.3... configure: WARNING: unrecognized options: --with-compiler checking for gcc... /usr/bin/gcc checking whether the C compiler works... yes checking for C compiler default output file name... a.out checking for suffix of executables... checking whether we are cross compiling... no checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether /usr/bin/gcc accepts -g... yes checking for /usr/bin/gcc option to accept ISO C89... none needed checking whether GCC supports __atomic_ builtins... no configure: creating ./config.status config.status: error: cannot find input file: `ghc-prim.buildinfo.in' libraries/ghc-prim/ghc.mk:4: recipe for target 'libraries/ghc-prim/dist-install/package-data.mk' failed make[1]: *** [libraries/ghc-prim/dist-install/package-data.mk] Error 1 Makefile:122: recipe for target 'all' failed make: *** [all] Error 2 I think it is fixed by saying 'sh validate' (i.e. start from scratch). But that is slow. I'm not 100% certain about the circumstances under which it happens, but can anyone help me diagnose what is going on when it does? Thanks SImon