Scarce attention has been paid to unstressed pronouns in haber `to be' existential clauses. Some of their semantic and syntactic properties hence remain largely unexplored. In this paper, the hypothesis is put forth that this clitic is a partitive or quantitative pronoun, which cliticizes the quantitative head of a partitive construction, that is, the pivot of haber . Evidence in this respect are pronouns found with some unaccusative verbs such as existir `to exist', faltar `to lack', presentative estar `to be' or abundar `to abound', which are here compared with Catalan, Italian, French, and Aragonese partitive clitics. The definiteness effect, which bars definite or specific pivots, also supports the claim that the clitic related to the pivot position cannot be definite.