We argue that ill-conditioned processes do not necessarily preclude the use of decoupling control. This applies also if the process is ill-conditioned in the crossover frequency range of a diagonal controller. Therefore the rule that one should never use a decoupler for ill-conditioned plants is misleading. The investigation is based on a discussion of the performance sensitivity of ill-conditioned systems and observations made from analyzing a semi-realistic model of a distillation column.