The paper deals with the pronominal paradigm of Mojeño, an Arawak language spoken in Bolivia. This paradigm is found as a formative of independent pronouns, person prefixes and suffixes on verbs and nouns, demonstratives, articles. The pronominal paradigm is particularly rich in third person categories, with on the one hand an unspecified third person form and on the other hand a set of forms distinguished according to humanness, number, gender and gender of the speaker. This paper will first show that, while most Mojeño pronominal forms can be traced back to Proto-Arawak, some third person forms (and the category they embody) do not easily compare with reconstructions (Payne 1987) or data in sister languages (Danielsen 2011). Morphophonemics hints at a recent development. The combination of old and recent forms results in a complex pronominal system, with a typologically remarkable third person subject indexation system on verbs, conditioned by co-arguments (Rose 2011). It will then be shown that there is no evidence for internal grammaticalization leading to the innovative forms. Finally, the paper will explore the idea that the innovative forms / categories may have risen through contact. It is traditionally asserted that personal markers are among the most stable elements of the language’s morphology. Some rare cases of borrowed pronouns are yet attested (Matras 2009), and some pronominal categories like inclusive/exclusive are reportedly borrowed. Within the contact hypothesis, the distinction between male and female speech for third person masculine will particularly be discussed. This kind of distinction has often been linked with catastrophic contact situations (Taylor 1980, Rodrigues 2004). Mojeño indeed has a very rich contact history, particularly as a lengua general during the Jesuit Missions period (Saito 2009). However, no source language has been identified up to now for the pronominal categories / forms under study.