Mixed-heritage individuals (MHIs) are known to face high levels of social exclusion. Here, we investigate how raciolinguistic ideologies related to one's heritage language abilities add to these exclusionary experiences. The results from 293 MHIs reveal frequent experiences of marginalisation from members of each of their heritage communities because their racial appearance and language practices are perceived as deviant and outside imagined 'monoracial' norms. Specifically, over half of respondents described experiences of exclusion for not speaking their minority heritage languages with the same accent or manner or fluency associated with 'monoracial' native speakers of their heritage languages or dialects. Another subset described high pressure to speak 'proper English' in White dominant work environments. These results extend past MHI work by empirically documenting the 'monoracial-only', monoglossic, and 'Standard English' ideologies that contribute to the continued social exclusion of MHIs.