Aims and objectives: While previous research has shown that phonetic variation in language contact situations is affected by whether a word has a cognate in the contact language, this paper aims to show that such an effect is not monotonic. According to the usage-based model, items in memory are organized according to similarity, thus we anticipated that formally more similar cognates would show a stronger cognate effect. Methodology: This variationist sociophonetic study investigates the relationship between cognate similarity and phonetic realization. We examined this relationship in the bilingual community of Rivera, Uruguay, in which both Portuguese and Spanish are spoken with regularity. Specifically, we focused on intervocalic /d/, which in monolingual Spanish is realized as an approximant [ð̞] or phonetic zero, but in monolingual Brazilian Portuguese is produced as a stop [d] or, in most varieties, an affricate [ʤ] before [i]. Data and analysis: We analyzed a corpus of sociolinguistic interviews of the Spanish spoken in Rivera. Acoustic measurements were taken from approximately 60 tokens each from 40 different speakers. Using a linear mixed-effects model, we examined the relationship between several predictors and the degree of constriction of intervocalic /d/. Findings/conclusions: While there is an overall frequency effect whereby more frequent words exhibit less constriction of intervocalic /d/, as both frequency and cognate similarity increase, less constriction of intervocalic /d/ obtains. Therefore, frequent cognates in Portuguese that have very similar forms affect the production of intervocalic /d/ more so than other cognates. Originality: No previous study has demonstrated that the cognate effect on phonetic variation in a situation of language contact is regulated by form similarity between cognate pairs. Significance/implications: The data support the usage-based model in that similar cognates have more lexical connections and can therefore show greater influence on phonetic realization than can cognates that share less phonetic material.