Šmartno is a critically endangered dialect of Slovenian that exhibits three interacting processes: final devoicing, unstressed high vowel deletion and vowel–glide coalescence. Their interaction is opaque: final obstruents devoice, unless they become final due to vowel deletion; high vowels delete, but not when created by coalescence. These patterns constitute a synchronic chain shift that leads to two emergent contrasts: final obstruent voicing and vowel length (due to compensatory lengthening). The paper examines all nominal paradigms, and complements them with an acoustic analysis of vowel duration and obstruent voicing. This work presents one of the most thoroughly documented instances of counterfeeding opacity on environment.