yi darcs crashes ghc 6.11.20090201

Building yi-0.5.3...
[  1 of 107] Compiling System.FriendlyPath ( System/FriendlyPath.hs, dist/build/System/FriendlyPath.o )
[  2 of 107] Compiling Shim.ProjectContent ( Shim/ProjectContent.hs, dist/build/Shim/ProjectContent.o )
WARNING: file simplCore/SimplCore.lhs line 545
Simplifier still going after 4 iterations; bailing out.  Size = 4969

[  3 of 107] Compiling Parser.Incremental ( Parser/Incremental.hs, dist/build/Parser/Incremental.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 6.11.20090201 for x86_64-unknown-linux):
        ASSERT failed! file typecheck/TcTyFuns.lhs line 286
[Wanted t_a89i{tv} [tau] :: a{tv a89b} [sk]
                              ~
                            a{tv a89a} [sk] -> t_a89h{tv} [tau]]