This paper investigates whether auxiliary selection and ne-cliticisation with intransitive verbs, two phenomena pertaining to the lexicon-syntax interface, can be fully acquired in Italian as the L2. It reports the findings of an experimental study in which a group of highly proficient adult L2 learners of Italian, in whose native language, Croatian, the two phenomena are not instantiated, and a group of Italian native speakers performed a speeded acceptability judgement. The results of the analysis of acceptability judgements and response times show that, despite their overall lower degree of determinacy, the intuitions of the L2 learners about the lexical-semantic and/or syntactic properties of the two phenomena converge on those of the native speakers. This suggests that the L2 learners have acquired the two phenomena to a similar degree as the native speakers. Such findings are in line with the hypothesis predicting complete attainment of interface properties involving syntax and another domain within the language faculty (i.e., the so-called properties relating to internal interfaces), in this case the lexicon.