This paper presents a description and a theoretical analysis of agreement within coordination in Lamaholot (Austronesian), where the first conjunct agrees with the conjunction ‘and’. Conjunctive agreement is obligatory in the subject position but is optional in the object position. The analysis is couched in terms of markedness of case and proposes that the case of the subject (nominative) is unmarked compared to the case of the object (accusative), and that only unmarked case enables phi-features of the agreement control to be copied onto the agreement host. Apparent optionality is accounted for by manners of case spreading in coordination. Conjunctive agreement is also reported in the genetically unrelated but areally related language of Walman. Although conjunctive agreement originates in verbal agreement with the comitative function in both languages, it is shown that grammaticalization from the comitative to the conjunction is more advanced in Lamaholot, at least in terms of syntax and morphology.