The present investigation focuses on first language (L1) and second language (L2) speakers' sensitivity to lexical fixedness and compositionality of Italian word combinations. Two studies explored language users' intuitions about three types of word combinations: free combinations, collocations, and idioms. In Study 1, Italian Verb+Noun combinations were embedded in sentential contexts, with control conditions created by substituting the verb with a synonym. L1 and L2 speakers rated sentence acceptability. In Study 2, the original verb was removed from sentences. Participants chose the verb from the list provided they felt was most acceptable. Computational measures were used to measure compositionality of word combinations. Mixed-effects modelling revealed that L1 and L2 speakers judged target word combinations differently in terms of lexical fixedness. In line with phraseological models, L1 speakers judged the use of a synonym as less acceptable in collocations than free combinations. On the contrary, L2 learners judged the use of a synonym as more acceptable in collocations than free combinations. However, all participants perceived idioms as least flexible of the three combination types. Results further showed an interesting effect of compositionality on the speakers' intuitions about the use of word combinations. Taken together, the findings provide new insights into how L1 and L2 speakers perceive word combinations that vary along the continua of lexical fixedness and compositionality.