§1. A marriage which is invalid because of a defect of consent is convalidated if the party who did not consent now consents, provided that the consent given by the other party perseveres.
§2. If the defect of consent cannot be proven, it is sufficient that the party who did not consent gives consent privately and in secret.
§3. If the defect of consent can be proven, the consent must be given in canonical form.
Source: Code of Canon Law (Vatican.va)