In several varieties of spoken Spanish, word-medial, labial stops are articulated as velar stops (pepsi > Pe[k]si). This work summarizes some previous attempts to explain this abrupt sound substitution. Then, building upon advances in phonotactic theory (e.g., Pierrehumbert, 1994) and patterns emergent from lexical representations (Bybee, 2001), this work presents a new theoretical perspective from which to examine the p > k phenomenon. Syllable-final, word-medial, velar stops (/g, k/) have a significantly higher token and type frequency than syllable-final, word-medial labial stops (/b, p/) in Spanish. As a result, the schema [..C VELAR$C..], and not [..C LABIAL$C..], emerges as a stronger, more productive schema, promoting the abrupt sound substitution LABIAL > VELAR.