Semitic languages are typologically unusual in making extensive morphological use of so-called “root-and-pattern” morphology, in the form of fixed-length templates that fix vowel qualities in the output while ignoring the vowels of the input. The expansion of Arabic over the past 1500 years has created ideal conditions for the borrowing of fixed-vowel fixed-length templates into the languages of massively bilingual minority groups in the Arab world. Prominent among the morphemes borrowed in such circumstances is the comparative/superlative template ʔaCCaC, conventionally termed the elative. This template has become fully productive in languages including Siwi Berber, Western Neo-Aramaic, and Mehri, and suppletively productive in Domari. A nearly exhaustive examination of massively bilingual minority groups in the Arab world suggests that the outcome is determined not only by sociolinguistic factors but also by structural ones: only languages with pre-existing triliteral fixed-vowel templates – used in particular for change-of-state verbs – borrow this template in a fully productive fashion, while other languages, if they borrow it at all, are forced to resort to suppletion and/or to leave it unproductive. This observation is consistent with two more broadly generalisable explanations: that the productive borrowing of “root-and-pattern” morphology requires not only the borrowing of its outputs but also the presence (through borrowing or common inheritance) of enough of the corresponding inputs, and that, in any given category, pre-existing root extraction processes are a precondition for the productive borrowing of “root-and-pattern” morphology.