For a large proportion of Mexican Indigenous speakers, it is common for the use of their native languages to shift across generations towards Spanish, the majority language in Mexico. This specific population can be defined as heritage speakers (HS) of their indigenous language, since many of them are Spanish-dominant bilinguals with a strong connection to their minority native language and culture, both of which they might only maintain in their family home where they were raised. The present study investigates the perceptual sensitivity of HS of Santiago Mexquititlán Otomi (Hñäñho) towards sounds of their native language to examine if these HS can accurately categorize Hñäñho vowels or whether their categorization is influenced by their dominant Spanish vowel system. Twelve Hñäñho HS (HHS) and twelve Mexican Spanish monolinguals (MSM) listened to the Hñäñho-specific vowel contrasts/a – ɔ/and/ɔ – o/and categorized them among the vowels of their respective mother tongue. Our results indicate that HHS correctly categorize vowels/a/and/o/, which exist in both Hñäñho and Spanish, but do not accurately categorize the Hñäñho-specific vowel/ɔ/. Moreover, HHS and MSM showed similar patterns in terms of the proportion of/ɔ/categorized as either/a/and/o/. These results have implications for the maintenance of language-specific vowel contrasts and the vowel system of a minority language, such as Hñäñho, in the context of language shift towards Spanish in Mexico.