Prove that if a is a primitive root mod p^2, then it is a primitive root mod p.

I have no idea where to go with this. I know that if a is a primitive root mod p^2 then: ord(mod p^2) a = phi(p^2) = p(p - 1), and a^(p(p-1)) = 1 mod p^2.

Where do I go from here?