Continuous process for preparing an isocyanate with a target production capacity of isocyanate, expressed as the mass flow rate, of m 1, target, with at least one change in the target production capacity m 1, target, comprising the reaction of the amine corresponding to the isocyanate with phosgene in a reaction space, in which (i) the amine is fed to the reaction space with a mass flow rate m 2 and phosgene to the reaction space with a mass flow rate m 3, wherein (ii) m 2 and m 3 are always chosen such that phosgene is present in excess relative to the primary amino groups of the amine, wherein (iii) in the at least one change in the target production capacity m 1, target, which is conducted from a starting state m 1, target ≠ 0 with a corresponding amine mass flow rate m 2, target and a phosgene mass flow rate m 3, target selected with regard to (ii) to a final state m 1, target # 0 with a corresponding amine mass flow rate m 2, target and a phosgene mass flow rate m 3, target selected with regard to (ii), where the change in the target production capacity m 1, target is by a value in the range from 10% to 90%, based on m 1, target, and where the change in the target production capacity m 1, target from the starting state m 1, target ≠ 0 to the final state m 1, target ≠ 0 is effected within a transition period t Ü which is at least 0.50 minute and at most 3 hours, the mass flow rates of amine m 2 and phosgene m 3 are altered during the transition period between the starting state and final state in such a way that (iii-1) the instantaneous phosgene excess at the point in time in the transition period at which the alteration of the mass flow rate m 2 from m 2, target to m 2, target is commenced is at least as high as and preferably greater than the phosgene excess during the period of production with the production capacity m 1, target prior to commencement of the transition period, and that (iii-2) the average phosgene excess during the transition period is greater than the phosgene excess during the period of production with the production capacity m 1, target prior to commencement of the transition period, where the phosgene excess during the production with the production capacity m 1, target prior to commencement of the transition period is equal to the phosgene excess during the production with the production capacity m 1, target after the end of the transition period. (i) the amine is fed to the reaction space with a mass flow rate m 2 and phosgene to the reaction space with a mass flow rate m 3, wherein (ii) m 2 and m 3 are always chosen such that phosgene is present in excess relative to the primary amino groups of the amine, wherein (iii) in the at least one change in the target production capacity m 1, target, which is conducted from a starting state m 1, target ≠ 0 with a corresponding amine mass flow rate m 2, target and a phosgene mass flow rate m 3, target selected with regard to (ii) to a final state m 1, target # 0 with a corresponding amine mass flow rate m 2, target and a phosgene mass flow rate m 3, target selected with regard to (ii), where the change in the target production capacity m 1, target is by a value in the range from 10% to 90%, based on m 1, target, and where the change in the target production capacity m 1, target from the starting state m 1, target ≠ 0 to the final state m 1, target ≠ 0 is effected within a transition period t Ü which is at least 0.50 minute and at most 3 hours, (iii-1) the instantaneous phosgene excess at the point in time in the transition period at which the alteration of the mass flow rate m 2 from m 2, target to m 2, target is commenced is at least as high as and preferably greater than the phosgene excess during the period of production with the production capacity m 1, target prior to commencement of the transition period, and that (iii-2) the average phosgene excess during the transition period is greater than the phosgene excess during the period of production with the production capacity m 1, target prior to commencement of the transition period, where the phosgene excess during the production with the production capacity m 1, target prior to commencement of the transition period is equal to the phosgene excess during the production with the production capacity m 1, target after the end of the transition period.