Fibonacci word check

checkFibWord :: [Char] -> Bool
checkFibWord [] = False
checkFibWord xs = if (len==y) then aux xs ys else False where
  len = length xs
  (y:ys) = makeFibLenList len
  aux "a" [] = True
  aux "b" [] = True
  aux "ba" [1,1] = True
  aux zs (n1:n2:ns) = 

    ((take n2 zs) == (drop n1 zs)) && (aux (take n1 zs) (n2:ns))
  aux _ _ = False

makeFibLenList :: Int -> [Int]
makeFibLenList len = aux 1 1 [] where
  aux a b xs
    | a >= len = (a:xs)
    | otherwise = aux b (a+b) (a:xs)


makeFibWord :: Int -> [Char]
makeFibWord 0 = "a"
makeFibWord 1 = "b"
makeFibWord n = if (n<0) then "a" else aux 2 "ba" "b" n where
  aux wnum w1 w0 num
    | (wnum==num) = w1
    | otherwise = aux (wnum+1) (w1++w0) w1 n