This study tests the hypothesis that alternation patterns with strong lexical support are more robust than those with no, or weak, lexical support. Focusing on three alternation patterns in Korean with varying productivity and generality, we measured lexical support in two ways. First, we conducted an acceptability-rating experiment investigating Korean speakers’ judgements on non-words with and without violations of the phonotactic constraints motivating the alternations. In addition, we performed a simulation of learning a maximum entropy (MaxEnt) Harmonic Grammar from a dictionary corpus. The results of the experiment and computational modelling confirmed the hypothesis by showing that if an alternation is robust, its associated phonotactic constraint is learned with a high weight from the MaxEnt simulation, and it affects the participants’ well-formedness ratings for non-words. Consequently, the results of this research support the claim of a tight link between alternations and phonotactics.