There was a thread here in March 2010 about issues with building regex-posix on Windows: http://www.haskell.org/pipermail/libraries/2010-March/013321.html It was pointed out that the maintainer doesn't have Windows access, and some conclusion seems to have been reached that allowed regex-posix to be included in the Haskell platform release. But it does not look as if the results were fed back to the maintainer for inclusion in the regex-posix package (darcs or hackage version). What is the recommended way to build regex-posix on Windows these days? Could the information be distilled into a package that builds without hacks, and could the hackage package please be updated to reflect that? It is a platform package, after all. Claus It looks as if at some point the package could just be built without external dependencies (other than GHC's build system) but it is not clear to me what the current intention is for building on Windows. The hackage version is still missing bits from the darcs version (in particular, the c-code to build and link with/include from), the darcs version has Makefiles that date back to when regex-posix was built within GHC's build system, and a configure.ac proclaiming the library to be at version 0.71. The .cabal file (version 0.94.2) features two Build-type entries (Custom and Simple), the Setup.hs simply calls defaultMain.