In this work the auto-tuning procedure proposed by Astrom and Hagglund is extended and developed for tuning the scaling factors of a modified hybrid PID type fuzzy logic controller (MHPID-FLC). This new procedure is based on two steps. First, mathematical expressions to link the scaling factors of the MHPID-FLC with the proportional, integral and derivative actions of its traditional counterpart are derived. Second, based on this relationship and using the Ziegler-Nichols tuning formulae, the scaling factors of the MHPID-FLC are obtained by means of a relay experiment. The effectiveness of this approach is shown in benchmark processes taken from the literature.