A missing signature is not always enough. The Czech Supreme Court comments on formal written-form clauses in contracts.

Contracts frequently contain provisions requiring certain actions to be made in writing. This typically applies to amendments to a contract or contractual addenda.

The requirement of a written form certainly serves an important purpose. It contributes to legal certainty and helps prevent disputes over what the parties actually agreed upon. However, in its judgment, Case No. 23 Cdo 2565/2024, dated 27 August 2025, the Czech Supreme Court emphasised that even a contractual requirement for a written form should not be interpreted mechanically or without regard to the parties’ subsequent conduct.

The case concerned a construction contract for building works. The contract provided that the works were to be completed within 120 days from the written handover of the construction site, evidenced by a formal handover protocol. However, no such protocol was ever signed. Despite this, the contractor took possession of the construction site in practice and commenced the works.

The lower courts dismissed the client’s claim on the grounds that the contractual completion period had never started to run because the required written handover protocol had not been executed. According to those courts, the contractor could therefore not be considered to be in delay.

The Supreme Court set aside that conclusion. It held that the courts should not have relied solely on the fact that the agreed written form had not been observed. They should also have examined how the parties actually behaved after the contract had been concluded. In particular, the contractor’s actual takeover of the construction site and the commencement of the works could be relevant in determining whether, in practice, the parties had followed a different procedure from the one originally described in the contract.

Although the judgment specifically concerned a construction contract, its significance extends beyond that particular type of agreement. The same reasoning may also apply to other contractual relationships in which the parties agree that certain amendments, instructions,

orders or handover procedures must be made in writing. Ultimately, it may not be only the wording of the contract that matters, but also the subsequent conduct of the parties.

The Supreme Court thereby reaffirmed an important principle: a party to a contract cannot always simply rely on the failure to comply with a formal requirement if that party has previously behaved in a way that led the other party to reasonably rely on an informal course of dealing. A typical example is where a party performs or accepts performance under a modified arrangement without objection and only later argues that a written amendment, written confirmation or another formal document was missing.

This does not, of course, mean that written-form clauses in contracts lose their importance. On the contrary, they remain an important tool for ensuring legal certainty. However, the Supreme Court’s judgment demonstrates that formal contractual provisions cannot be relied upon in a manner that is inconsistent with the principles of good faith and mutual trust between the contracting parties.

The practical lesson for contractual relationships is straightforward. If a contract requires a written protocol, amendment, order, confirmation or any other formal procedure, it is advisable to comply with that requirement. If, however, the parties choose to proceed differently, they should be aware that their actual conduct may also have legal significance.

Whenever there is uncertainty regarding the performance of a contract, it is therefore important to consider not only the wording of the contract itself, but also the subsequent communication and the actual conduct of both parties. These circumstances may ultimately determine whether one party is entitled to rely on the failure to comply with the agreed formal requirements, or whether such an argument would be inconsistent with that party’s previous conduct.

If you are involved in a contractual dispute, dealing with the other party’s delay in performance, the validity of a contract termination, or the question of whether a particular arrangement between the parties was effectively agreed, we will be pleased to help you assess your legal rights and the options available in your particular situation.

Mgr. Anna Kateřina Ondráčková, Junior Attorney

Mgr. Jana Sedláčková, Attorney at law, Partner

Pajerová Sedláčková ADVOKÁTKY s.r.o.

30.7.2026