A model is presented to calculate the influence of ferroelectric/ferroelastic domain switching near a crack tip on the effective fracture toughness of piezoelectric ceramics. The switch-toughening effect is quantified in terms of intrinsic field intensity factors accounting for residual fields within the fracture process zone which are due to constraints at the boundary of the switching zone. The intrinsic field intensity factors themselves depend on the external electromechanical loading of the cracked body and thus can clearly be expressed in terms of the intensity factors of the applied loading. These can also account for the effects of an electrical permeability of the crack. The extension of the process zone is calculated using closed-form solutions for the asymptotic crack tip fields in connection with a domain switching criterion. Subsequently, the amount of switch-toughening is calculated applying a weight function technique. Therefore, crack weight functions have been derived for the real anisotropy in piezoelectrics.