Short answer. If the mistake was mutual, either party may ask the court to correct the document, and so may their successors in interest. If only one side was mistaken or misled, only the injured party may ask, together with his heirs and assigns. The party who caused the error cannot.
What the law says
Reformation may be ordered at the instance of either party or his successors in interest, if the mistake was mutual; otherwise, upon petition of the injured party, or his heirs and assigns.
Civil Code, Article 1368 — Who May Seek Reformation. Read the full provision →
What reformation is — and what it is not
Reformation is the remedy for a document that says the wrong thing. The parties genuinely agreed on something; the written instrument, through mistake, fraud, inequitable conduct or accident, failed to record it. The court does not make a new bargain. It rewrites the paper so it finally expresses what the parties actually agreed on.
That distinction decides most petitions. If there was never a real meeting of minds, there is nothing to reform — the remedy is annulment, not correction. And if you simply regret the terms you agreed to, no court will improve them for you. Reformation fixes the record, not the deal.
Mutual mistake: either side may sue
Where both parties laboured under the same misunderstanding — the deed describes the neighbouring lot, the figures were transposed, the wrong parcel number was carried over from an old draft — Article 1368 of the Civil Code lets either party go to court. Neither is at fault, so neither is preferred.
The article also names successors in interest. This matters more than it looks. Buyers, assignees, heirs and anyone who acquired the rights under the contract can bring the petition, so a defect discovered years later by a new owner is not beyond repair merely because the original parties are gone or unwilling.
One-sided mistake: only the injured party
Where the error was not shared — one party knew the instrument did not reflect the agreement and stayed silent, or actively procured the wrong wording — only the injured party may petition, along with his heirs and assigns.
The reasoning is simple fairness. A person cannot benefit from his own fraud or inequitable conduct by asking a court to tidy up the document he engineered. He is bound by the paper he created, and only the person harmed gets to decide whether to correct it or to pursue some other remedy. Some contracts are excluded from reformation altogether, notably simple donations without a condition and wills.
Proving it, and the deadline
The burden on a petitioner is heavy, because a notarised instrument carries weight and the law presumes people meant what they signed. Clear and convincing evidence of the true agreement is needed — drafts, emails and messages during negotiation, survey plans, payment records, the conduct of the parties afterwards, and the testimony of whoever prepared the document.
There is also a prescriptive period for a written contract, counted from the time the right of action accrues, so delay can extinguish the remedy entirely. If you have found that a deed, mortgage or lease does not say what you agreed to, get the file and the correspondence to a lawyer promptly. No one can promise how a court will read the evidence, but the case is far stronger while the paper trail is fresh.