Reversed and remanded for entry of judgment in favor of appellants, Theodore and Mildred DuBois. Upon examination of the record we find that the guarantee in question is unambiguous and, as written, is prospective only in application. See Clermont Builders Supply, Inc. v. General *63Construction & Design, Inc., 423 So.2d 518 (Fla. 5th DCA 1982). Even if we were to find a waiver of the parol evidence rule and consider the parol evidence presented to the trial court, we find no competent, substantial evidence to support the trial court’s finding that the guarantee agreement was intended to cover prior debts.