Scholarship shows that Black immigrants to the United States resist assimilation to reduce exposure to racial discrimination faced by U.S.-born African Americans. But, not all Black immigrants are equally likely to be (mis)perceived as African American. We argue that immigrants who are likely to be misidentified as African American have incentives to reify ethnic boundaries as a form of protection against racial discrimination. We develop this argument from interviews and focus groups with African immigrants. We then use a lab experiment to measure rates of miscategorization and identify its correlates among African immigrants. Finally, we test our argument with a novel survey of Somalis, an immigrant population with two ethnic subgroups who differ in their likelihood of being miscategorized as African Americans. We show that this difference shapes the degree of resistance to assimilation. These findings improve our understanding of the relationship between racial discrimination and incentives for Black immigrants to resist assimilation.