I'm not sure I understand that bug at all! The unix package is supplied with GHC. You can't, in general, just use a different version. Haskell Platform 2012.4 ships with GHC 7.4.1, which includes unix-2.5.1.1. I wouldn't expect unix-2.6.x.y to work with GHC 7.4.1 at all. Of course unix-2.6.x.y works with GHC 7.6.z, as that is the version of GHC that distributes with it. For this release, I expect to package GHC 7.6.3 (essentially 7.6.2 plush one bug fix), which includes unix-2.6.0.1. In short - I don't see that that bug is anything but as expected, and there is no need for a fix - as unix-2.6.0.1 will come with the next HP. - Mark ​