Short answer. No. Article 801 of the Civil Code states that supervening incapacity does not invalidate an effective will, meaning a will validly made while the testator had capacity stays valid even if the testator later becomes mentally incapacitated. What matters legally is the testator's capacity at the moment the will was executed, not what happens to their capacity afterward.
What the law says
Supervening incapacity does not invalidate an effective will, nor is the will of an incapable validated by the supervening of capacity.
Civil Code, Article 801 — Supervening Incapacity. Read the full provision →
The rule locks in at the moment of signing
Article 801 says, in full, that supervening incapacity does not invalidate an effective will. The key word is supervening — incapacity that arises later, after the will was already validly made. If the testator had the capacity the law requires when they signed, and the will was an effective one at that moment, a later decline in mental capacity does not reach back and undo it. The will's validity is fixed at the time of execution, not continuously re-tested afterward.
The rule works the same way in reverse
The same article addresses the opposite situation too: nor is the will of an incapable validated by the supervening of capacity. If someone lacked capacity when they made a will, later regaining capacity does not retroactively cure the defect and make that earlier will valid. Read together, both halves of Article 801 point to a single principle: the testator's capacity is assessed at the moment the will is executed, and events before or after that moment do not change the answer.
What Article 801 does not itself define
Article 801 tells you when capacity matters, not what capacity actually consists of. It does not spell out here what mental state qualifies someone as capable of making a will in the first place, so whether a particular testator had the required capacity at signing is a separate, fact-specific question that this article alone does not resolve. What it does settle is that once that question is answered favorably at the time of signing, later changes in the testator's condition do not disturb the will.
Why the moment of signing is what to document
Because Article 801 anchors validity to the point of execution, disputes over a will made by someone who later became incapacitated tend to turn on what could be shown about the testator's condition on that specific day — not their condition months or years later when the will is being probated. Anyone concerned about a will being challenged on capacity grounds should focus on preserving whatever record exists of the testator's state at the time the will was actually signed.