This study addresses the question whether the borrowability of linguistic forms, in particular affixes, is constrained by structural properties of the donor and recipient languages involved. According to some claims, structural similarity favors affix borrowing. On some accounts, structural compatibility of a certain kind is even a precondition for affix borrowing. This study tests these claims using data from a set of 78 languages that borrowed between one and 50 affixes, taken from the AfBo database (Seifart, 2013a). The extent of affix borrowing in this set of languages is compared with structural similarity scores for the donor and recipient languages involved, obtained from morphosyntactic features provided in the World Atlas of Language Structures (Dryer and Haspelmath, 2011). Results suggest that structural similarity between a (potential) donor and recipient language plays at best a minor role in determining the extent of affix borrowing. This supports the view that bilingual speakers are not—at least not strongly—constrained by structural factors of the languages they speak when creating mixed varieties of these languages, resulting in contact-induced language change.