The Cantor-Leibler theory of macroscopic emulsion stabilization by adding diblock copolymer is reexamined with regard for the curvature of the equilibrium droplets. The treatment is based on the assumption that the equilibrium state of the system corresponds to adsorption of most diblock copolymer molecules at the interface which leads to a one-to-one correspondence between the average droplet size, R, and the interfacial area per copolymer molecule, Sigma. First we find R in the approximation of zero interfacial curvature and then investigate the equilibrium emulsion characteristics using the interfacial free energy expansion over the interfacial curvature (up to the second-order terms). The curvature effect is shown to lead to small corrections for R as calculated for the flat interface model. As a result, R does not depend strongly (inversely proportional) on the relative difference in copolymer block lengths unlike the results of the previous considerations of the emulsion stabilization. For the cases of a semidilute copolymer layer at the interface and the unpenetrable copolymer layer ("dry brush") the corrections due to the curvature effect are calculated explicitly. The conditions of a complete diblock copolymer adsorption at the interface are discussed.