In this article, we characterize the semantic contribution of the French negative marker ne in temporal clauses with avant 'before'. Traditionally considered semantically vacuous, ne is an example of expletive negation (EN), a negative marker that has been assumed to be null in meaning as it seems like it is not contributing to the calculation of the sentence meaning. In line with recent work that offered alternative approaches to a vacuous account of negative markers in other languages (Krifka 2010, Cépeda 2018b), we propose that EN ne plays a semantic role: it negates that Event A in the main clause holds while Event B in the avant-clause is taking place. Simply put, EN does express negation as it negates that A and B can overlap in time. We report on the preliminary results of two experimental studies designed to verify our hypothesis and show that EN does in fact have a negative semantics.