Prenuptial agreements may include a sunset clause which voids the agreement when your marriage lasts a certain amount of time.This clause can instore trust in your marriage and faith in your spouse that you believe the marriage will be a long and happy one and therefore the prenup will no longer be necessary.nnOne other scenario is that a prenuptial agreement is deemed not enforceable in Pennsylvania if the party opposing the agreement can establish, by clear and convincing evidence that the party did not execute the agreement voluntarily. Lack of full disclosure of assets is also a reason that a prenup can be voided. Finally, proof of duress or coercion to sign a prenup can also be a reason it may be voided.