Haskell Help

Haskell beginner here. Anybody know how i shrink this down a bit, sorry I'd figure out myself but i'm sick of learning the same concepts in 20 different languages.

{-

type Month = String

validMonth :: Month -> Bool
validMonth "January" = True
validMonth "February" = True
validMonth "March" = True
validMonth "April" = True
validMonth "May" = True
validMonth "June" = True
validMonth "July" = True
validMonth "August" = True
validMonth "September" = True
validMonth "October" = True
validMonth "November" = True
validMonth "December" = True
validMonth _ = False

-}

data Month = January | February | March | April | May | June
             | July | August | September | October | November
             | December deriving (Read, Show, Eq, Ord)