"class A where a :: A -> Int" panics GHC 6.4

Coming back to Haskell after a year off, I accidentally typed a very 
simple class definition wrong, and turns out that GHC 6.4 dies with 

ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
	ds_app_type Main.A{tc r1zQ} []

if you run

$ ghc crasher.hs
ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
	ds_app_type Main.A{tc r151} []

where crasher.hs is a file with a single line

class A where a :: A -> Int

I'm using the OSX version of GHC, by the way.

-carlos

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Trac field	Value
Version	None
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedDuplicate
Component	None
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