For copyright protection of computer programs, the computer program directive (Directive 2009/24/EC on the legal protection of computer programs) stipulates special rules on EU level, among them a rule for decompilation, according to which such decompilation does not require authorisation from the copyright owner where it necessary to achieve the interoperability with another program.
In a case remitted to the ECJ, the defendant had decompiled a program not for interoperability purposes, but to remove a program error (in order to deactivate a program part viewed as deficient).
The ECJ found that such a decompilation can already be justified by a more general exception provided for in the directive, which does not mention decompilation, but which allows i.a. the translation of a program if necessary for its intended purpose including error correction (judgment of October 6, 2021, case No. C-13/20 – Top System/Belgium; the judgment concerned a prior version of the directive which does, however, not differ from the current version in this regard). A prerequisite is, among others, that there is no contractual remedy for achieving the error correction.
It is thus clarified that interoperability is not the only purpose which can justify a decompilation.