This is a tricky question. The answer depends upon whether the agreement was voluntarily executed and whether or not the agreement is unconscionable. Certainly it is not good form to wait until the day before the wedding to execute a prenuptial agreement. If this occurs, and a party seeks to challenge enforcement of the prenuptial agreement, first, if there was not full disclosure of property, and if you are not represented by independent counsel, the agreement should be easy to attack and invalidate. Assuming you were represented by independent legal counsel, in all likelihood, your attorney witnessed you executing the agreement and executed a certificate acknowledging that you entered the agreement knowingly and voluntarily. The absence of that certificate of your independent counsel would likely make the agreement easy to attack. Finally, a prenuptial agreement can still be invalidated if it is found to be unconscionable.