As I am sure many people have noticed, there is currently a serious problem with FFI on 64-bit Windows. It often happens that when you link in FFI against a standard DLL, the resulting application segfaults as soon as any function from the DLL is called. I experienced this problem with Bryan's text-icu library when I linked it against the standard Windows 64-bit DLLs provided by the ICU project. In this case, the workaround I found is to link instead against DLLs built using mingw-w64 and provided as part of MSYS2: https://mail.haskell.org/pipermail/haskell-cafe/2015-May/119737.html On reddit, /u/awson (is that Kyra?) pointed out that this issue is probably caused by a serious bug in GNU binutils that was fixed about two months ago: https://sourceware.org/bugzilla/show_bug.cgi?id=16598 Is it possible to update the MSYS2/mingw-w64 toolchain used by GHC to a recent version that includes this fix? Thanks, Yitz