Small Haddock question

This is irritating me now... Suppose I have something like the following:

zero = 0 :: Int
one = 1 :: Int
two = 2 :: Int
three = 3 :: Int

How do I add Haddock comments to the end of each line? For some reason, 
Haddock doesn't like either of

zero = 0 :: Int -- | Zero
zero = 0 :: Int -- ^ Zero

Either way it whinges about parse errors. How do I make it shut up and 
stop being so dense at me? :-} It's damned obvious what I want it to do...