We construct the complete superspace action L of chiral D = 10, N = 2 supergravity. The self-duality condition on the field strength F(a1-a5) is derived as an equation of motion in superspace. The space-time restriction of L is not supersymmetric, since the self-duality condition does not follow from the space-time variational equations. However, supersymmetry can be restored via the introduction of a Lagrange multiplier term.