Here's an update to our efforts to get a working build of text-icu on Windows 64 bits: I am working together with Kyra on this on the café list. It is becoming clear that GHC is unable to use standard DLLs on Windows 64 bits. That means FFI is really broken on that platform at the moment. By "unable to use standard DLLs" I mean specifically this: When GHC creates an executable with FFI by linking against object files, the GHC runtime is unable to use the DLLs corresponding to the object files if those DLLs were created by standard Microsoft build tools and not MingW. It's not clear yet whether this incompatibility is due to a change in GHC, or a new incompatibility between MingW's binutils and Microsoft's native DLL tools. Currently I am trying create new ICU DLLs from the object files using binutils so that we can use text-icu. If successful, that will solve our particular problem in the short term. But it won't solve the problem of FFI on Windows 64 bits in general. Here is the bug report I submitted for text-icu, with a simple way to reproduce the problem: https://github.com/bos/text-icu/issues/12 Shall I report that as a GHC bug as well? Thanks, Yitz