This paper presents evidence from both corpora and agent-based simulation for the effect of lectal contamination. By doing so, it shows how agent-based simulation can be used as a complementary technique to corpus research in the study of language variation. Lectal contamination is an effect whereby the words that are typical of a language variety more often appear in a morphosyntactic variant typical of that same variety, even among language use from a different variety. This study looks at the Dutch partitive genitive construction, which exhibits variation between a “Netherlandic” variant with -s ending and a “Belgian” variant without -s ending. It is shown that the probability of the Belgian variant without -s increases among more “Belgian” words, in the language use of both Belgians and people from the Netherlands. Meanwhile, an agent-based simulation reveals the crucial theoretical preconditions that lead to this effect.