Whereas the intonation of Spanish varieties has received considerable attention in the past few decades, the research has so far not included the variety of Spanish spoken in Paraguay, where intensive language contact between the Indigenous Guarani language and Spanish since the 16th century has led to widespread bilingualism. This study compares the F0 patterns of yes/no questions in Guarani-dominant bilinguals with those of Spanish-dominant bilinguals and Spanish monolinguals, formalized within the Autosegmental-Metrical model of intonation phonology. Results show no particular differences between the three groups, with all groups producing an H+L*LH% pattern in all types of yes/no questions, the exception being counter-expectational and echo yes/no questions, which were also realized with an L+¡H* L% contour. In spite of the fact that Guarani-dominant bilinguals exhibited more tonal variation in biased yes/no questions, the findings appear on the whole to support the convergence of two intonational systems due to the long period of contact. Furthermore, both bilingual groups made use of Guarani question particles and other Guarani expressions in their productions. Interestingly, across all groups, some speakers occasionally used the calque expression ¿ Será que . . . (“Will it be that . . .?”) at the beginning of questions; this construction can be considered to have become grammaticalized as a question particle. Taken together, the intonational and syntactic innovations apparent in Paraguayan Spanish point toward language change brought about by intensive contact with Guarani and show how two levels of linguistic structure—intonation and syntax—may evolve differently.