Learning Haskell with Project Euler - Problem 2 (Fibonacci Sequence Sum with Limit)

fib.hs

-- Base formula, but this is exponential time
fib :: Int -> Int
fib 0 = 0
fib 1 = 1
fib x
    | x < 0 = error "No Negatives allowed"
    | otherwise = fib (x-2) + fib (x-1)

-- When doing an unbounded sequence, where should we stop?
fibLimit:: Int -> Int -> Int
fibLimit limit number
    | limit <= 0 = error "Really?"
    | number <= 0 = 0
    | fib number < limit = fibLimit limit (number+1)
    | otherwise = number-1

main = do 
    let maxFib = fibLimit 4000000 20
    print (sum [fib x | x <- [1..maxFib]])