Let A be a real (non-associative) algebra which is normed as real vector space, with a norm · deriving from an inner product and satisfying ac a c for any a, c ∈ A. We prove that if the algebraic identity (a((ac)a))a = (a 2 c)a 2 holds in A, then the existence of an idempotent e such that e = 1 and ea = a = ae , a ∈ A, implies that A is isometrically isomorphic to R, C, H, O, C, H, O or P. This is a non-associative extension of a classical theorem by Ingelstam. Finally, we give some applications of our main result.