The present study explores the elicited production of differential object marking and subject-verb inversion in matrix and embedded wh- questions in Spanish among 16 English-speaking L2 learners and 17 Spanish-speaking immigrants serving as control baseline. Results from an elicited production task show high levels of variability among the L2 learners, crucially with differential object marking in animate and specific contexts and with obligatory inversion in embedded wh- questions. Furthermore, our data show overall more difficulty with inversion in embedded questions than with differential object marking, suggesting that structural complexity, frequency and transfer from English may cause a structure not on an interface level to present more difficulties for advanced L2 learners in this case. The results are discussed along the lines of previous research on vulnerable domains, and the role of crosslinguistic influence, structural complexity and surface overlap in language development.