GTC control as a stumbling block - index clause violates transparency requirement

On 5 June 2025, the Düsseldorf Higher Regional Court (case reference: 10 U 146/24) declared a value protection clause in a commercial tenancy agreement to be invalid - with potentially far-reaching consequences for the drafting of contracts in commercial tenancy law.

The case centred on three key legal questions:

1. Is a price adjustment clause in a commercial lease additionally subject to a content review under general terms and conditions law in addition to the requirements of the Price Clause Act (PrKG)?
2. Particularly relevant in practice: Can a clause be ineffective because the rent adjustment is linked to an index date before the start of the tenancy?
3. And: Does the ineffectiveness of such a clause apply from the time it is determined by a court - or retroactively from the conclusion of the contract - with potentially significant repayment consequences for landlords?

How the judgement came about

The subject of the legal dispute was an index clause in a long-term commercial tenancy agreement. The parties had concluded a rental agreement on 28 August 2019 that provided for an automatic adjustment of the rent to the consumer price index - a common means of hedging against inflation and maintaining economic balance over the term of the agreement.

However, the specific wording of the clause was particularly striking: the month of May 2017 was agreed as the starting point for the index development - i.e. a date that was more than two years before the start of the tenancy on 1 September 2019.

The tenant was confronted with significantly higher rent payments during the course of the contract and considered the clause to be non-transparent and inappropriate. She sued for repayment of the overpaid amounts. The regional court ruled in favour of the claim and declared the clause invalid. The landlord appealed - without success: the Düsseldorf Higher Regional Court upheld the decision and dismissed the appeal.

Key statement 1: Value protection clauses are subject to general terms and conditions control

A central legal point of contention in the Düsseldorf Higher Regional Court's decision was the question of whether price adjustment clauses in commercial leases are also subject to a content review in accordance with Sections 307 et seq. BGB - and can therefore be invalid from the outset if they violate the transparency requirement.

This question has not yet been answered uniformly in case law and literature. While the Higher Regional Court of Schleswig, for example, assumes in a reference decision of 5 February 2024 (case no. 12 U 69/23) that the standards of review under Section 2 (1) no. 2 PrKG and Section 307 (1) sentence 2 BGB are identical and that the legal consequence of invalidity is based exclusively on Section 8 PrKG, other voices - especially in the literature - take the view that violations of Section 307 BGB lead to the clause being directly invalid in accordance with Section 306 BGB, irrespective of the PrKG.

The OLG Düsseldorf agrees with this latter view and thus takes a clear position in a previously unresolved opinion dispute. It emphasises that the review under general terms and conditions law is independent and supplementary to the special statutory review under the PrKG and is not superseded by it. This double review is not only permissible, but also necessary, as the two regulatory systems pursue different protection objectives: While the PrKG serves the public interest, in particular the protection against inflationary tendencies and the safeguarding of price stability, the review under GTC law is aimed at safeguarding contractual fairness between the parties. It examines whether the clause is formulated transparently and whether the interests of both contracting parties have been adequately taken into account. In the opinion of the Senate, this functional difference means that a breach of Section 307 BGB is not "absorbed" by the special statutory provision of the PrKG, but can independently lead to the invalidity of the clause.

This means that not only the invalidity of the value adjustment clause, but also the reversal of rent adjustments that have already been made - with considerable financial risks for landlords.

Key statement 2: Ineffectiveness due to index date before the start of the tenancy

Another aspect of the decision concerns the time reference within the rent adjustment clause at issue: The parties had agreed that the starting point for the index development should be the month of May 2017 - i.e. a point in time that was more than two years before the start of the tenancy on 1 September 2019.

The Higher Regional Court of Düsseldorf therefore had to examine whether this temporal link - i.e. the choice of an index level outside the contractual period - could in itself lead to the clause being invalid, for example due to a lack of transparency and a lack of comprehensibility of the basis for calculation.

The court denied the validity of the clause with reference to Section 307 (1) sentence 2 BGB and judged it to be non-transparent. The tenant was unable to recognise how the initial rent was calculated in concrete terms, as the relevant index level at the start of the contract was not apparent.

In addition, the court considered the choice of an index date before the start of the lease to be an unreasonable disadvantage for the tenant: any price increases between May 2017 and September 2019 were solely to her detriment, although she had not received any consideration from the landlord during this period - in particular no grant of use. This constellation contradicts the principle of equivalence of performance and consideration and, in the court's opinion, renders the clause invalid.

In support of its reasoning, the OLG referred to Section 2 (3) No. 3 PrKG, which expressly mentions the stipulation of an index date prior to the start of the lease as a standard example of unreasonable disadvantage. As a result, the court declared the clause invalid as a whole. It is therefore also interesting to note that the OLG Düsseldorf uses the PrKG as a standard of assessment for the judgement of a possible violation of general terms and conditions.

The economic relevance of this decision is particularly clear for project developers and landlords who work with long-term commercial leases - for example in development projects that are planned "from the drawing board" and where the start of the lease is often far in the future. In such cases in particular, there is a great temptation to set index values at an early stage in order to gain costing certainty. However, the judgement shows that such a practice can be legally risky. The clause is not only invalid for the past, but also has no effect for the future - it is null and void overall. In economically strained times, when many project developers are under pressure anyway, this can lead to considerable financial burdens.

Key statement 3: Time of invalidity

The clarification of the Düsseldorf Higher Regional Court with regard to the point in time of the invalidity of the value protection clause at issue is also significant. While Section 8 PrKG generally stipulates that a clause in breach of the PrKG only becomes ineffective (ex nunc) once it has been legally established by a court, the OLG ruled in the present case that in the event of a breach of Section 307 BGB, ineffectiveness occurs from the outset (ex tunc) - i.e. from the conclusion of the contract.

The Senate rejected the partially held view that an inappropriate clause is initially only "pendingly ineffective" and only loses its effect upon judicial determination. Such a view would allow landlords to use unreasonably disadvantageous clauses without risk - a result that is not compatible with the protective purpose of Section 307 BGB. The regional court had also already correctly determined that Section 8 PrKG had never had the function of keeping a clause "provisionally" effective that was ineffective under the law on general terms and conditions.

This interpretation has considerable practical consequences: Landlords cannot claim to have acted lawfully until the court decision. Instead, there is a threat of repayment claims for all rent adjustments made over the years, subject to any statute of limitations that may have occurred.

The decision thus emphasises the importance of legally secure contract drafting and calls for particular care when formulating price adjustment clauses - especially in long-term tenancies.

Outlook and recommendations for practice

The decision of the Düsseldorf Higher Regional Court has far-reaching practical consequences for the practice of contract drafting in commercial tenancy law. In future, landlords will have to check much more carefully whether their value retention clauses not only fulfil the requirements of the PrKG, but also meet the strict standards of general terms and conditions control in accordance with Section 307 BGB. The transparency of the clause, the comprehensibility of the calculation basis and the temporal consistency of the index reference points are particularly critical. Clauses that refer to an index level before the start of the lease or whose calculation mechanism is not clearly recognisable for the tenant are legally vulnerable and can be declared invalid retroactively (ex tunc) and trigger repayment claims for rent adjustments already made - with sometimes considerable financial consequences for landlords. Existing commercial leases in which similar clauses were used are particularly affected.

In practice, it is therefore urgently recommended that existing contracts be comprehensively reviewed from a legal perspective and, if necessary, replaced with legally secure supplementary agreements. Particular care should also be taken with new contracts: The choice of index date, the calculation basis and the comprehensibility of the clause must be clearly and unambiguously regulated.

It is also advisable to closely follow further developments at the highest court - in particular a possible decision by the Federal Court of Justice. The appeal has been authorised as the underlying legal question - whether and to what extent the General Terms and Conditions Control applies in addition to the PrKG - has not yet been decided by the highest court. A decision by the Federal Court of Justice could follow and further clarify or even recalibrate the legal situation.