The US Supreme Court in the case Hall Street Associates, L.L.C. v. Mattel, Inc. decided that the grounds to vacate, modify or correct arbitration awards under the Federal Arbitration Act could not be expanded by agreement of the parties. The Court’s decision raises the question as to how this issue would be dealt with in other jurisdictions. This Article analyses whether the legal grounds for setting aside international awards rendered in Spain may be expanded by the parties, or whether they may exclude them or waive the right altogether.