Control of the energy‐dependendent second‐order aberrations in a Mattauch‐type mass spectrometer is made difficult by the absence of a real image between the object slit and the focal plane in this resolving system. By curving the boundary of the magnetic field and by choosing appropriate relations between the magnetic field boundary curvature and the other parameters involved, it is possible to make both of the energy‐dependent second‐order aberration coefficients vanish simultaneously while retaining the advantages peculiar to this resolving system.