In Asturian and in Central-South Italian dialects there is a category of indefiniteness expressed by a set of properties involving Mass singular and indefinite plural nouns, determiners, pronouns; furthermore, the Mass/Count distinction is revealed by a number of plural markers, which are also semantic counters. This set of properties originally goes back to the Latin neuter and to partitive constructions introduced by the Latin preposition DE ‘of’ + ablative. Romance languages set up new strategies following the loss of Latin case-marking, especially the loss of the inflected Latin neuter (see Alonso 1958; Hall 1968; Penny 1970; Lüdtke 1988; Arias Cabal 1998), which generate a set of constraints to express indefiniteness in grammar. Depending on the Romance language, the ‘new’ grammatical category of indefiniteness widely involves Mass singular nouns, indefinite plurals, such as heteroclite nouns in Italian (e.g. Italian il braccio ‘the arm’, le braccia ‘the arms’), in Central-South Italian dialects and in Rumanian (e.g. lucrul ‘the thing’, lucrurile ‘the things’), articles, pronouns, etc. that are recognized by different markers (see Russo 2002, 2009, 2021, 2022; Kihm 2007; Maiden 2016; Curchi 2022; Burner 2023). The grammar of indefiniteness is settled down by a bunch of morphosyntactic and phonological properties that hold the ‘neutrals’ relations in phrases: Mass nouns and plural indefinite combined with indefinite plural determiners, with uncountable adjectives, neutral pronominal clitic objects, heteroclite nouns, and metaphonic alternations. Metaphony is crucial in Asturian and Italian dialects to signal gender and number, the Mass/Count contrast with internal affixes with or without a final plural-marking. This development has strong effect on (verbal and nominal) agreement in Romance. In this talk, we focus on the grammatical markers set off by Asturias to express indefiniteness and their interaction with Asturian metaphony. In Asturias the Mass/Count distinction includes inflectional /-o/ opposed to /-u/ (Mass nouns opposed to masculine nouns), such as the following Mass Ns (see DGLA): fégado‘liver’ (Llena, Carreño, Asuries Central, Bimenes, Llangréu, Casu, Ayer, Los Argüeyos) fierro‘iron’ (Llangréu, Riosa) trigo‘wheat’ and trío (Llangréu)(Cabu Peñes) Those nouns with inflectional /-o/ show uncountable agreement in Noun Phrases with adjectives (see DGLA): negro ‘black’ Mass is opposed to the masculine and metaphonic masculine variant nigru (Bimenes, Llangréu, Ayer, Llena, Riosa) seco ‘Mass’ is opposed to metaphonic masculine variant sicu (Ayer, Llena, Riosa) muito vino ‘much wine’ (Cangas del Narcea) The clitic object -lo (Mass) is also opposed to -lu (M): llu M vs. llo Mass (Ayer) u M vs o Mass (Sobrescobiu) The metaphonic effect in Asturian is triggered, as for Italian dialects, by final high vowels and it involves the tonic mid-vowels /e o/ and the back vowel /a/ (see Arias Cabal 1998). In this talk, we will sketch the Mass/Count distinction in Asturian at the morphology/phonology/ lexicon interface for cross-linguistic comparison with Central-South Italian dialects. We will describe the indefiniteness and plural marking of Asturian, in which plural markers metaphoninc and non-metaphonic are semantic counter. Crucially, we found that Mass/Noun distinction correlates with number inflection, Asturian and Italian dialects independently developed a way to express plurality in count masculine nouns involving metaphony, and they had convergent evolution. We assume that the Mass/Count distinction is based in the lexicon, but it is implemented by the syntax and the phonology. References Academia de la llingua asturiana, 2001(19981). Gramática de la Llingua Asturiana, Oviedo, Academia de la Llingua Asturiana. Alonso, D. (1958). Metafonía y neutro de materia en España (sobre un fondo italiano). ZRP 74:1-24. Arias Cabal, Á. (1998). 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