Let I(X, K) be the incidence algebra of a finite connected poset X over a field K and D(X, K) its subalgebra consisting of diagonal elements. We describe the bijective linear maps ϕ : I(X, K) → I(X, K) that strongly preserve the commutativity and satisfy ϕ(D(X, K)) = D(X, K). We prove that such a map ϕ is a composition of a commutativity preserver of shift type and a commutativity preserver associated to a quadruple (θ, σ, c, κ) of simpler maps θ, σ, c and a sequence κ of elements of K.