Haskell : Use -XFlexibleContexts to permit this?

My code as follows:

calcstep ::Integral a => a -> acalcstep  n = calcstep2 n 0calcstep2 :: Integral (Integral a, Integral b) => a -> b -> acalcstep2 1 k = kcalcstep2 n k | odd n = calcstep2 (n/2) (k+1)              | otherwise = calcstep2 (n*3+1) (k+1)

The error is as follows:

Non type-variable argument

in the constraint: Integral (Integral a, Integral b)

(Use -XFlexibleContexts to permit this)

In the type signature for `calcstep2': calcstep2 :: Integral (Integral a, Integral b) => a -> b -> a

Failed, modules loaded: none.

What does it mean? how can I fix it?