  We construct a minimal example of a supersymmetric grand unified model in a
toroidal compactification of type I string theory with magnetized D9-branes.
All geometric moduli are stabilized in terms of the background internal
magnetic fluxes which are of "oblique" type (mutually non-commuting). The gauge
symmetry is just SU(5) and the gauge non-singlet chiral spectrum contains only
three families of quarks and leptons transforming in the $10+{\bar 5}$
representations.
