The protection afforded by Article 1341, paragraph 2, of the Civil Code cannot operate in favour of the party which has unilaterally predisposed the contract containing the arbitration clause, since that provision is directed to protecting the contracting party who suffers the application of the contractual regulation and not the party who predisposes and inserts the clauses in the contract.
The prohibition against venire contra factum proprium prevents the party which has inserted an arbitration clause in a contract which it has unilaterally predisposed from subsequently contesting its effectiveness for lack of specific written approval, in application of the duty of good faith and contractual fairness.