The European Court of Justice (ECJ) ruled on 6 October 2021 in Top System SA v. Belgian State (Case C‑13/20) EU:C:2021:811 that, under article 5(1) of the Software Directive (Council Directive 91/250/EEC) (the Directive), lawful purchasers of software are permitted to decompile programs (in whole or in part) in order to correct errors affecting the software’s operation.

Case background

The decision comes as the result of a request for a preliminary ruling by the Brussels Court of Appeal. The request had been made in proceedings between Top System SA and the Belgian state concerning the decompilation by the Selection Office of the Federal Authorities in Belgium (SELOR) of a computer program developed by Top System and forming part of an application in respect of which SELOR holds a user licence.

What the Directive says

Article 4 of the Directive deals with “Restricted Acts” that give developers exclusive rights to reproduce and alter computer programs, whereas article 5 allows the licensor to reproduce and alter a program where necessary to use it for its intended purpose, including for error correction. Article 6 deals with decompilation, permitting the reproduction of software code and translation where doing so is indispensable to obtain the information necessary to achieve interoperability so long as: it is done by the licensee or other authorised person; the information necessary to achieve interoperability is not readily available to the licensee; and any related actions taken are limited to those portions of the original software/computer program necessary to achieve interoperability.

Decompilation: ECJ’s ruling

In Top System, the ECJ ruled that under an interpretation of article 5 the lawful purchaser of a computer program is entitled to decompile the program (in whole or in part) in order to correct errors affecting its operation, without being required to satisfy the requirements of article 6. The licensee would not be allowed to use the decompiled software for any other purpose than error correction.

Advocate general’s opinion

The advocate general’s opinion on the case confirmed that a licensee could decompile a computer program to correct errors, unless restricted by the licence. The opinion emphasised the independence of articles 5 and 6, and the possibility of decompilation under article 5, as well as article 6. Specifically, the opinion stated that article 5, independent of article 6 (which permits decompilation), should be interpreted as permitting a licensor to decompile a computer program where necessary to correct errors affecting its functioning.


 The lesson from this ECJ ruling is that a computer program can be decompiled where necessary to fix an error under article 5 and that that right is independent of the article 6 right to decompile a program when necessary for interoperability. While the case should not be seen as opening the floodgates for decompiling software by a licensor, it does offer helpful clarity as to the rights and obligations of both the licensor and licensee when it comes to managing software errors.

To limit disputes around the decompilation of licensed software, the ECJ has advised that the procedure for correcting software errors should be addressed in the licence and contract provisions. Although the parties are not permitted to exclude the possibility of correcting errors altogether, a contractual arrangement will allow licensees and licensors to find a method best suited to the objectives of each party.