We propose a natural S 4 × SO(10) supersymmetric grand unified theory of flavour with an auxiliary Z 2 4 × Z R 4 symmetry, based on small Higgs representations (nothing larger than an adjoint) and hence a type-I seesaw mechanism. The Yukawa structure of all fermions is determined by the hierarchical vacuum expectation values of three S 4 triplet flavons, with CSD3 vacuum alignments, where up-type quarks and neutrinos couple to one Higgs 10, and the down-type quarks and charged leptons couple to a second Higgs 10. The Yukawa matrices are obtained from sums of low-rank matrices, where each matrix in the sum naturally accounts for the mass of a particular family, as in sequential dominance in the neutrino sector, which predicts a normal neutrino mass hierarchy. The model accurately fits all available quark and lepton data, with predictions for the leptonic CP phase in 95% credible intervals given by 281 • < δ < 308 • and 225 • < δ < 253 • . The model reduces to the MSSM, with the two Higgs doublets emerging from the two Higgs 10s without mixing, and we demonstrate how a µ term of O(TeV) can be realised, as well as doublettriplet splitting, with Planck scale operators controlled by symmetry, leading to acceptable proton decay.