What Happens If a Prenup Is Partially Invalid?

A single flawed clause does not always sink an entire prenuptial agreement. Depending on how the agreement is written and how serious the flaw is, a Washington court may strike the bad provision and enforce the rest, or it may throw out the whole thing.

One Bad Clause Does Not Automatically Void Everything

When a prenup is challenged, the fight is often over a specific term rather than the entire document. Maybe one clause tries to waive spousal support in a way that is grossly unfair, or attempts to control something a prenup cannot control, or was slipped in without proper disclosure. The question then becomes whether that one problem contaminates the whole agreement or can be isolated and removed.

Washington courts generally have two paths. The first is severance: the court cuts out the invalid provision and enforces the remaining terms, treating the agreement as if the bad clause were never there. The second is voiding the entire agreement: if the problem goes to the heart of the deal, the court refuses to enforce any of it and falls back on the default property rules. Which path a court takes depends on whether the agreement is severable and on how fundamental the unfairness is.

When a Court Can Sever and Save the Rest

Severability is the idea that a contract can be split into independent parts, so that removing one part leaves the others standing on their own. If a prenup's clauses are genuinely independent, a court can strike an invalid or unconscionable provision and still enforce the balance. For example, if a property division clause is fair, fully disclosed, and voluntary, but a separate clause tries to do something impermissible, a court may be able to enforce the property terms while ignoring the improper one.

This is much easier when the agreement itself anticipates the possibility. Many well drafted prenups include a severability clause, a provision stating that if any part of the agreement is found invalid, the rest remains in effect. That clause signals to the court that the parties intended each provision to stand alone, which supports salvaging the valid terms. Even without such a clause, a court may sever where the provisions are logically separable and removing the bad one does not distort the bargain the parties actually struck.

When the Whole Agreement Falls

Severance is not always available. Sometimes the flaw is not a single stray clause but a defect that runs through the entire agreement, and in that situation a court will void the whole thing. This turns on the same fairness analysis Washington uses to judge prenups generally.

That analysis comes from In re Marriage of Matson, 107 Wn.2d 479 (1986). Under Matson, a court first asks whether the agreement makes a fair and reasonable provision for the spouse who is not seeking to enforce it. If it does not, the court asks whether that spouse nonetheless entered into it freely and knowingly, with full disclosure of the other's property and independent advice about the rights being given up. When the failure occurs at that level, the whole agreement is in jeopardy, not just one clause. If there was no real financial disclosure, or the signature was not voluntary, the defect infects everything. You cannot sever your way out of an agreement that was never entered into knowingly in the first place.

The timing cases make the point vivid. In re Marriage of Bernard, 165 Wn.2d 895 (2009), involved an agreement presented to one spouse only days before the wedding, with a substantially revised version arriving right before the ceremony. The court found the process itself unfair, and the entire agreement was invalidated. That was not a problem a court could fix by editing out one line. The unfairness went to how the whole agreement came to be signed, so the whole agreement fell.

Fundamental Unfairness Versus a Fixable Flaw

The practical dividing line is between a localized problem and a fundamental one. A localized problem lives in a single, separable clause while the rest of the agreement was fair, disclosed, and voluntary. That is the classic candidate for severance. A fundamental problem, by contrast, taints the formation or the core fairness of the entire deal: no disclosure, coercion, or an agreement so one sided that enforcing any of it would be unconscionable. Those defects tend to sink the whole document.

There is also a middle reality worth naming. Courts do not enjoy voiding entire agreements when the parties clearly intended to plan responsibly, so where the terms are otherwise sound and the parties plainly meant to be bound, judges will often look for a way to preserve what is fair. But that instinct only goes so far. If the foundation is rotten, no amount of judicial goodwill will save the structure.

The Lesson for Anyone Drafting or Relying on a Prenup

For couples in Snohomish County, the takeaway cuts two ways. If you are drafting a prenup, build it to survive partial challenges: keep provisions clean and independent, include a thoughtful severability clause, and above all make sure the whole agreement rests on genuine disclosure, fair terms, and a voluntary, unhurried signing so no fundamental defect can bring it all down. If you are the spouse questioning a prenup in a divorce, understand that your challenge might knock out one clause or the entire agreement depending on where the flaw lies, and that difference can dramatically change how your property is divided.

Either way, the analysis is fact specific and rarely obvious from the four corners of the document alone. If you have a prenuptial agreement you are worried about, or you want one drafted so that a single issue will not unravel the whole thing, the Law Office of Chad Foster works with clients across Snohomish County. Reach out to have your agreement reviewed before it is ever tested in court.