English nouns that are borrowed into Korean as ending in [t] are lexicalized as if they ended in /s/. While some researchers have suggested that the lexicalization of word final [t] as /s/ reflects a general weakening process or involves something specific to loanwords, we will argue that the borrowing of English word final [t] as lexical /s/ in Korean is purely a matter internal to the morphophonology of Korean. While our claim is not a new claim since the idea is present in some of the recent literature, the detailed analysis of this within Optimality Theory and its formal connection to cases of paradigm leveling elsewhere in Korean nominal morphology as well as to diachrony is original.