This study examines a case of an identical sound shift, /u/-fronting, in both the majority (Multicultural Toronto English, Denis et al. 2013) and heritage (Seoul Korean, Kang 2016) languages in Toronto. Linear mixed effects models of the spontaneous speech of heritage (n = 16) and homeland (n = 10) Seoul Korean speakers show that Generation is not a predictor of participation in the vowel shift. In addition, heritage speakers share significant predictors of vowel shift participation that are not attested in English. A second shift, /o/-raising, is investigated as a counterpoint variable, as it is only attested in Seoul Korean but not Multicultural Toronto English (Kong and Kang 2018). Heritage speakers also participate in this shift, showing similar patterns to homeland speakers. Together, these point to Korean influence, not English interference, in heritage speakers’ participation in the vowel shift in heritage Korean.