In this contribution we discuss the consequences of the contract when it has been modified in a substantial manner. On a European level there has been provided in the sanction of the ineffectiveness of the contract, which procedure can be initiated within six months after the change has happend. In Belgian law there is also the sanction of the annulment of the contract, whereby the contract can be declared null, which can be invoked even after the six month period, thus it seems. In this contribution we formulate some critical remarks on the situation in Belgium.
Keywords: substantial modifications, sanction of annulment, sanction of ineffectiveness