This paper proposes an account of nasalization phenomena in Xochistlahuaca Amuzgo (XA), a variety of Guerrero Amuzgo, using insight from the phonology-morphology interface within the context of constraints due to monosyllabic lexical roots. Previous assumptions are clarified to show that while nasal consonants and vowels exist phonemically, complex nasal-stop segments do not; and nasalization remains limited to root morphology and a set of inflectional markers and does not occur across syllable boundaries, in contrast with Mixtecan languages. These insights are illustrated by the third-person singular human enclitic (3SGHUM), a nasal autosegment. Alternations triggered by 3SGHUM show that complex nasal-stop segments are shown to be allophones of simple nasals that are post-oralized before an oral vowel to protect and enhance nasal-oral contrast in vowels, an example of the phenomenon known as shielding. A reduplicative allophone of 3SGHUM further displays nasalization that appears exceptional when compared with other nasalization phenomena in plural and pronominal inflection, as well as derivation. These challenges are met from a strict CVCV approach, enabled by the assumption that the Proto-Amuzgo-Mixtecan *CVCV lexical root survives today in XA as CCVV(ʔ), the maximal lexical root. The monosyllabic economy that sets XA apart from its sister languages influences strategies that block against morphophonological change triggered by inflection, or that enhance contrast against loss of identity. Enhancing strategies like shielding then bring XA into a typological relationship with unrelated languages (Jê, Tupí-Guarani, among others).