impossible internal bug while building darcs

[ghc] src/Exec.o
ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.1 for i386-unknown-linux):
        applyTypeToArgs
    unix-2.3.1.0:System.Posix.Signals.a38{v r8P} [gid]
      (unix-2.3.1.0:System.Posix.Signals.a5{v r8O} [gid]
       `cast` (ghc-prim:GHC.Prim.sym{(w) tc 34v}
                 base:Foreign.C.Types.:CoCInt{tc r4P}
               :: <pred>base:GHC.Int.Int32{tc 3V}
                          ~
                        <nt>base:Foreign.C.Types.CInt{tc r4S}))
      unix-2.3.1.0:System.Posix.Signals.Ignore{v r8N} [gid]
      (base:Data.Maybe.Nothing{v r4K} [gid]
         @ <nt>unix-2.3.1.0:System.Posix.Signals.SignalSet{tc r8M})
      eta{v a1Vy} [lid]
    (# ghc-prim:GHC.Prim.State#{(w) tc 32q}
         ghc-prim:GHC.Prim.RealWorld{(w) tc 31E},
       <nt>unix-2.3.1.0:System.Posix.Signals.SignalSet{tc r8M} #)

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

While building darcs 2.2.0.