The instructions at https://ghc.haskell.org/trac/ghc/wiki/Newcomers were slightly outdated, and result in a rather confusing error messsage: $ ./sync-all --testsuite get Unrecognised flag: --testsuite at ./sync-all line 872. == Checking for old haddock repo == Checking for old binary repo == Checking for old mtl repo == Checking for old Cabal repo == Checking for old time from tarball ============================ ATTENTION! You have an old time package in your GHC tree! Please remove it (e.g. "rm -r libraries/time"), and then run "./sync-all get" to get the new repository. ============================ == Checking for obsolete Git repo URL $ The patch corrects the error message. I've removed the --testsuite flag from the wiki page as well.