package authors, I'm preparing to release two new versions of cabal-install. The following packages are broken, and the new cabal-install releases will mean that more users run into the breakage than do so currently. All these packages claim to work with base 3 *and* with base 4, however they actually only work with base 3. The new cabal-install will build them against base 4 and so users will notice that they are broken. I'm emailing the whole libs list because while I was able to build most of hackage, I could not build all of it, so there may be other packages with this same problem. FileManipCompat-0.14 type-level-0.2.3 compact-string-0.3.1 ghc-core-0.5 hsmtpclient-1.0 pointful-1.0.1 show-0.3.3 These packages all use "build-depends: base >= 3 && < 4" (except for ghc-core which cheekily uses "build-depends: base < 10" --- a practise we will ban if it becomes any more popular). Current versions of cabal-install choose base version 3 in this case, the new cabal-install will choose base version 4 in this case. The reason for the somewhat odd current behaviour was to help with packages that only said "build-depends: >=3". Now that we require an upper bound too, the new behaviour is to only apply the backwards compat preferences for version ranges that are unbounded above. For ones that are bounded above we go back to picking the highest version by default. Duncan