haskell cant get it to work...

error

test.hs:6:60: error:
    • Couldn't match expected type ‘a1’ with actual type ‘a2’
      ‘a2’ is a rigid type variable bound by
        the type signature for:
          isPrimeHelper :: forall a2. Integral a2 => a2 -> Bool
        at test.hs:5:29-68
      ‘a1’ is a rigid type variable bound by
        the type signature for:
          isPrime :: forall a1. Integral a1 => a1 -> Bool
        at test.hs:3:15-48
    • In the second argument of ‘mod’, namely ‘n’
      In the first argument of ‘(/=)’, namely ‘number `mod` n’
      In the expression: number `mod` n /= 0
    • Relevant bindings include
        n :: a2 (bound at test.hs:6:43)
        isPrimeHelper :: a2 -> Bool (bound at test.hs:6:29)
        number :: a1 (bound at test.hs:4:23)
        isPrime :: a1 -> Bool (bound at test.hs:4:15)
  |
6 |                             isPrimeHelper n = number `mod` n /= 0
  |

test.hs

findPrimes :: Integral a => [a] -> [a]
findPrimes numbers = [x | x <- numbers, isPrime x]
	where isPrime :: Integral a => a -> Bool
              isPrime number = all (isPrimeHelper) [2..number-1]
		      where isPrimeHelper :: Integral a => a -> Bool
	                    isPrimeHelper n = number `mod` n /= 0