This article argues that the central vowel /ɘ/ in Shiwilu, a language from the Peruvian Amazon, is non-moraic. In response to its non-moraic status, the syllable onset following /ɘ/ geminates in order to satisfy a syllable well-formedness condition requiring that every syllable has a mora. Phonological and phonetic data provide evidence for both the non-moraic status of this central vowel and the gemination repair strategy. We propose that unlike in most languages displaying mora augmentation, gemination in Shiwilu is not driven by a stress-to-weight constraint; rather, it is motivated by the combination of high-ranked constraints prohibiting non-moraic syllables and moraic non-low central vowels. The Shiwilu case fills a typological gap by instantiating a pattern predicted to occur given reranking of constraints independently needed to derive attested interactions between moraicity and prosodic headedness.