This looks like a hugs bug to me - GHCi gets it right. Inflate> 4294967295 :: Word32 4294967295 Inflate> (4294967295 :: Word32) > 0 True Inflate> array (0, (4294967295 :: Word32)) [] // [(5, 98)] array Program error: {_out_of_bounds (0,-1) 5} Inflate> Incidentally, how do you get the Word and Array modules in scope at once without using a module to import them both? My fiddling with :l and :a wasn't fruitful. Thanks Ian