On 6 July 2022 the UK Supreme Court delivered its judgment in Basfar v. Wong, a case regarding the application of the “commercial activity” exception enshrined in Article 31, paragraph 1 (c), of the Vienna Convention on Diplomatic Relations. This landmark decision offers an innovative interpretation of that provision to the effect that diplomatic agents do not enjoy immunity in relation to the employment of domestic workers under circumstances amounting to modern slavery. After focusing on the interpretation of the exception concerning “commercial activity”, exception endorsed in previous case-law, this paper aims at assessing whether the new interpretation of this exception is justified in present-day international law.