This study investigates the knowledge of bilingual speakers of Catalan and Spanish regarding the production of object pronominal clitics (excluding non-reflexive third-person clitics), with a focus on: (i) their morphology, considering the variants that coexist for each form, and (ii) their syntactic placement (proclitic or enclitic) with respect to the verb. We present results from a study of thirty-nine simultaneous bilingual Catalan-Spanish speakers, residents of several geographic areas of Majorca, Spain, including the capital, Palma, and several villages. The speaker data came from a spontaneous oral production task carried out separately in each one of the two languages. We also analyze historical data from a diachronic corpus of Catalan to evaluate whether clitic properties of the Catalan produced by bilinguals constitute grammatical innovations in the language. The results indicate that bilingual speakers of Majorcan Catalan mostly acquire archaic forms for clitics (proclitics and enclitics) that also match the corresponding form of Majorcan Spanish clitics. We interpret these results as showing an effect of bilingualism with Spanish that has contributed to the preservation of archaic forms in the grammar of bilingual speakers of Catalan in Majorca because these forms partially match the ones found in Spanish.