panic (the impossible happened) when compiling with -O2

when compiling the attached program with -O2 I get the following error:

[1 of 1] Compiling Main             ( crashTest.hs, crashTest.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.4 for i386-apple-darwin):
	Coercion.splitCoercionKindOf
    ghc-prim:GHC.Prim.left{(w) tc 34B}
      (ghc-prim:GHC.Prim.trans{(w) tc 34y}
         (List-0.3:Data.List.Class.ItemM{tc r28}
            (List-0.3:Control.Monad.ListT.ListT{tc r34}
               (ghc-prim:GHC.Prim.(->){(w) tc 3D} a{tv ayS} [sk]))
            (List-0.3:Control.Monad.ListT.ListT{tc r34}
               (ghc-prim:GHC.Prim.(->){(w) tc 3D} a{tv ayS} [sk]) c{tv ayR} [sk]))
         (ghc-prim:GHC.Prim.(->){(w) tc 3D} a{tv ayS} [sk]
          List-0.3:Control.Monad.ListT.:CoF:R5ItemM{tc r29} List-0.3:Control.Monad.ListT.ListT{tc r34}
                                                              (ghc-prim:GHC.Prim.(->){(w) tc 3D}
                                                                 a{tv ayS} [sk])
                                                              c{tv ayR} [sk]))
    <pred>List-0.3:Data.List.Class.ItemM{tc r28}
            (List-0.3:Control.Monad.ListT.ListT{tc r34}
               (ghc-prim:GHC.Prim.(->){(w) tc 3D} a{tv ayS} [sk]))
            ~
          ghc-prim:GHC.Prim.(->){(w) tc 3D} a{tv ayS} [sk]

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

When compiling without -O2, it works. I am using TypeFamilies (for the List class)

Trac metadata

Trac field	Value
Version	6.10.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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