Basic Fibonacci function using Word causes ghci to panic. - 6.10.1

When inputting the function:

let fib :: Word -> Word; fib 0 = 1; fib 1 = 1; fib n = l + r where l = fib (n-2); r = fib (n-1)

GHCi produces a panic error:

ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.1 for i386-apple-darwin):
	schemeE(AnnCase).my_discr __word 0

It has been confirmed on both OS X 10.5.5 and linux

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture	x86