Can you have two patents for the same invention?

In Belgium, yes—at least on paper: the Intellectual Property Office grants patents without a substantive examination, so there is nothing to prevent the same applicant from obtaining two patents for the same invention. Enforcing both patents is another story. That is the key conclusion of the report written by the Belgian group of AIPPI, the International Association for the Protection of Intellectual Property, on double patenting and divisional applications (rapporteurs A. Bouten and C. Dumont) in preparation for the World Congress in October 2026. Here’s a summary of the key points.

Why the Belgian Patent Office does not prevent double patents

In practice, Belgian patent law functions as a registration system. The Intellectual Property Office checks the formal requirements and conducts a novelty search, but does not reject an application on the grounds that the invention is not new or not inventive. Therefore, anyone who files the same invention twice will receive two patents.

The legislature has never addressed this issue with a general ban. No provision of the Code of Economic Law (CEL) states that the same applicant may hold only one patent per invention. The issue only comes before a court after the patent has been granted, either when a competitor challenges the validity of one of the two patents or when the holder seeks to enforce both of them.

The only legal obstacle: the Belgian patent takes a back seat to the European one

The legislature has, however, provided for one specific situation: the coexistence of a Belgian patent and a European patent. According to Article XI.86 of the CEL, a Belgian patent ceases to have effect as soon as three conditions are met. The same inventor or his assignee obtains a European patent; that patent covers the same invention and the same territory; and both share the same filing date or, if priority is claimed, the same priority date.

The effective date is fixed. If no opposition is filed against the European patent, the Belgian patent ceases to have effect upon the expiration of the opposition period; if an opposition is filed, the Belgian patent ceases to have effect on the date the proceedings conclude with the European patent being maintained. The Intellectual Property Office does not make this determination itself. Only the Business Court of Brussels can determine whether the Belgian patent has lost its effect in whole or in part.

The decision that elevated a ban to a general legal principle

On September 28, 2021, the Dutch-speaking Business Court in Brussels went a step further. The court ruled that two patents for a single invention cannot be granted to the same applicant—not on the basis of a statutory provision, but as a general legal principle. It drew inspiration from the case law of the Enlarged Board of Appeal of the European Patent Office, in particular decision G 4/19.

The decision drew criticism from legal scholars. Notably, the claims of the two patents in that case were not strictly identical; the wording differed. The ruling leaves open exactly what “the same applicant” and “a single invention” mean. The Belgian AIPPI group maintains that a prohibition applies, in any case, to situations where the scope of protection of both patents is strictly identical; according to the group, anything described as “essentially the same” opens the door to legal uncertainty.

How the European Patent Office rejects identical applications

The situation is different for European patents. In the decision G 4/19 of June 22, 2021, the Enlarged Board of Appeal confirmed that a European patent application may be rejected on the basis of Articles 97(2) and 125 of the European Patent Convention (EPC) when it claims the same subject matter as a European patent that has already been granted to the same applicant and does not form part of the prior art. The guidelines for examination of the European Patent Office explicitly incorporate that prohibition.

However, the scope remains limited. The prohibition prevents the granting of a second patent for the same invention, not the holding of two patents that have already been granted. And “the same subject matter” is interpreted strictly in the commentaries: it refers to identical claims, not to two patents that claim the same invention in different words (J. Mazurelle, EPI Information March 2023, 23). In practice, therefore, a slight difference in wording is enough to circumvent the ban. That is why one scholar called the ban a “paper tiger”.

Spin-off applications: flexible, but only until the date of approval

A divisional application separates a portion of a pending patent application and continues it as an independent application, while retaining the original filing date. This becomes mandatory when the application violates the principle of unity of invention (Art. XI.19, § 1 CEL): more than one invention, or multiple inventions lacking a common inventive concept, necessitates limiting or dividing the application.

Belgian regulations are flexible. According to Article 18, § 1 of the Royal Decree of December 2, 1986 with regard to the filing, granting, and maintenance of invention patents, a divisional application may be filed until the date of grant of the pending parent application. There is no limit on the number of divisional applications, and cascades are permitted: a divisional application may itself serve as the basis for a subsequent divisional application (Art. 19, § 2 of the same decree). The procedure requires nothing more than the identification of the parent application number; a justification for the division is not required. The same logic applies to the European Patent Office: a division may be filed as long as the prior application is pending, that is, until the day before the publication of the notice of grant.

Where the divisional game becomes an abuse

That flexibility has a downside. On October 31, 2024, the European Commission imposed a fine of 462.6 million euros on the pharmaceutical company Teva in Case AT.40588 concerning the MS drug Copaxone. The basic patent expired in 2015. Teva subsequently filed a series of divisional applications covering the manufacturing process and dosage regimen, sought preliminary injunctions against generic competitors based on those applications, and strategically withdrew the patents as soon as they were threatened with invalidation. In this way, the company avoided setting a precedent that would have invalidated the rest of the patent family, while competitors were forced to initiate new proceedings time and again.

The Belgian AIPPI group draws a twofold lesson from this. Filing divisional applications is never, in and of itself, an abuse; the assessment falls under competition law, with the specific circumstances of the case serving as the benchmark. However, Belgian law does have its own instrument at its disposal: the prohibition against abuse of rights, enshrined in Article 1.10 of the Civil Code (CC). Anyone who exercises a right in a manner that clearly exceeds the limits of what a prudent and reasonable person would do in exercising that right is abusing that right.

Legal scholars have already suggested that Belgian case law could take this approach. Some members of the AIPPI group view the prohibition against abuse of rights under Article 1.10 of the Belgian Civil Code as the basis for accepting, under Belgian law, an equivalent to the English “Arrow declaration”: a negative declaration of law that provides an alleged infringer with legal certainty against a cascade of spin-offs. Belgian courts have not yet taken that step. The group does, however, point out the drawback of any ex post remedy: by the time the court finds abuse, the competitor’s market entry has already been delayed, and all that remains is a claim for damages that is difficult to prove.

Specifically, what does this mean?

For patent holders. It is possible to obtain two patents for the same invention in Belgium, and this can even be useful—for example, when one patent is pledged as collateral and the other remains available for licensing. However, keep Article XI.86 of the CEL in mind: if you validate a European patent for the same invention in addition to your Belgian patent, the Belgian patent loses its effect. And anyone who actively uses a portfolio of divisional applications in legal proceedings would be well advised to have the threshold for abuse of rights reviewed in advance by a lawyer specialized in patent law.

For competitors and generic players. A cascade of spin-offs is not an insurmountable barrier. The Teva Copaxone decision shows that competition law intervenes when filing and withdrawing applications becomes a market-fencing strategy, and Article 1.10 of the Belgian Civil Code provides a legal basis for challenging such conduct. Document the chronology of filings, withdrawals, and proceedings: it was precisely that pattern that led to the fine of 462.6 million euros.

Frequently asked questions (FAQ)

Does my Belgian patent automatically expire when I obtain a European patent?
Not automatically in the sense that a registry is updated. Article XI.86 of the CEL provides that a Belgian patent ceases to have effect as soon as the same inventor or his successor in title obtains a European patent for the same invention and the same territory, with the same filing or priority date. Only the Business Court of Brussels can determine whether those conditions are met and whether the lapse affects the patent in whole or in part.

How many spin-off applications can I submit?
There is no limit, neither in Belgium nor at the European Patent Office. The only strict requirement is the time frame: the parent application must still be pending. In Belgium, this means filing before the grant date of the parent application; at the European Patent Office, it means filing up to the day before the publication of the notice of grant. Furthermore, a divisional application can itself serve as the basis for a subsequent divisional application.

Conclusion

Belgian law does not provide for a general prohibition on double patenting. The only statutory provision, Article XI.86 of the Code of Economic Law, addresses the overlap between a Belgian and a European patent, and the 2021 court decision that established a broader prohibition as a general legal principle remains contested. Divisional applications are broadly permitted in Belgium, without limit and in a cascade, but anyone who uses them as a defensive weapon runs afoul of competition law and the prohibition against abuse of rights under Article 1.10 of the Civil Code. For patent strategies in Belgium, the question is therefore rarely whether it is allowed, but rather how far it can go.