The granting of State aid without prior approval by the Commission is unlawful and exposes the beneficiaries to possible recovery measures. However, it may be difficult to determine whether a measure constitutes State aid within the meaning of Article 107(1) TFEU. In the energy sector, a typical difficulty is in determining to what extent a regressive tax qualifies as a selective aid measure. In order to avoid all risk, it is best to notify the measure if there is any doubt as to its qualification. Although this seems a very simple rule of thumb, it is one that Member States very often fail to understand. Unfortunately, Belgium is no exception to that.