panic while compiling Cabal-1.6.0.1

While compiling Cabal-1.6.0.1, as packaged with Cabal-0.6.0, I got:

[16 of 50] Compiling Distribution.Simple.Utils ( Distribution/Simple/Utils.hs, dist/build/Distribution/Simple/Utils.o )
ghc-6.8.2: panic! (the 'impossible' happened)
  (GHC version 6.8.2 for x86_64-unknown-linux):
        applyTypeToArgs
    unix-2.3.0.0:System.Posix.Signals.a38{v rov8} [gid]
      (unix-2.3.0.0:System.Posix.Signals.a5{v rov7} [gid]
       `cast` (base:GHC.Prim.sym{(w) tc 34v}
                 (base:Foreign.C.Types.:CoCInt{tc r1dN})
               :: <pred>base:GHC.Int.Int32{tc 3V}
                          ~
                        <nt>base:Foreign.C.Types.CInt{tc r17X}))
      unix-2.3.0.0:System.Posix.Signals.Ignore{v rov6} [gid]
      (base:Data.Maybe.Nothing{v r6E} [gid]
         @ <nt>unix-2.3.0.0:System.Posix.Signals.SignalSet{tc rov5})
      eta{v apCg} [lid]
    (# base:GHC.Prim.State#{(w) tc 32q}
         base:GHC.Prim.RealWorld{(w) tc 31E},
       <nt>unix-2.3.0.0:System.Posix.Signals.SignalSet{tc rov5} #)