Let A 0 (Γ2) denote the ring of scalar-valued Siegel modular forms of degree two, level 1 and even weights. In this paper, we prove the determinant of a basis of the module of vector-valued Siegel modular forms k≡ mod 2 A det k ⊗Sym(j) (Γ2) over A 0 (Γ2) is equal to a power of the cusp form of degree two and weight 35 up to a constant. Here j = 4, 6 and = 0, 1. The main result in this paper was conjectured by Ibukiyama (Comment. Math. Univ. St. Pauli 61 (2012) 51-75).