Opinion by
Mr. Chief Justice Bell,Plaintiff brought an action in equity to enjoin the erection of a second building upon a tract of land which defendant had purchased from Mary E. McWilliams.
On April 15, 1959, the nominees of the parties entered into an agreement of sale for a tract of 1.1 acres on the south side of Presidential Boulevard North in Lower Merion Township, Montgomery County, Pa. The Agreement provided, inter alia:
“12. Buyer agrees to improve the site with an* office building; final plans and specifications for said building to be subject to the approval of the Owner, ■ which approval shall not be unreasonably withheld.”
On July 13, 1959, the property was conveyed to the defendant and on July 22,1959, she applied for a building permit to erect an office building on the property in accordance with a plan which had been approved by the plaintiffs. The permit was granted and the building has been erected.
On January 3, 1961, defendant filed a plan for subdividing her tract. This plan was withdrawn because it would require a special exception. Thereafter, a new subdivision plan was filed which was approved by the municipal authorities, and defendant filed a new application for a building permit to erect a second building upon the aforesaid 1.1 acre tract. This permit was also granted by the township. Thereupon plaintiffs brought the present equitable action.
Plaintiffs at the trial of this suit asked one of their witnesses “What was your discussion with Mr. Strouse?”** Defendant's objection to this was sustained. Plaintiffs then offered to prove that prior to the written Agreement the parties intended the word “an” to mean “only one” office building and that *634throughout the negotiations for a sale of the property —as well as in the written Agreement itself — that was the intention of the parties as shown by their conversations and by certain correspondence which we note, parenthetically, did not support plaintiffs’ contentions. The offer of proof was rejected by the Court and this is the basis for the appeal.
The Chancellor filed an adjudication and decree nisi in which he dismissed plaintiffs’ complaint and ordered judgment to be entered for the defendant. Plaintiffs filed no exceptions to the Chancellor’s findings of fact, but excepted to his conclusions of law and to the Court’s Order and Decree.
If the parties had intended to limit the land to one office building it would have been very easy to have used the word “one”. The Agreement contains no such restriction, nor any affirmative promise by the buyer to build only one office building. The fact that the buyer originally built an office building in compliance with the Agreement of Sale does not prove that the Agreement restricted buyer to only one office building or compelled her to erect on the land only one office building. Since the defendant-appellee agreed to improve the site with an office building which met with the approval of the plaintiffs-appellants, the obligation imposed by that provision of the contract has been complied with and ceases to have any further force and effect. To attempt to interpret the provision of the agreement as a perpetual covenant running with the land would impose restrictions on the future use of the land and impinge upon its alienability. Clear and explicit language is required to impose such a restriction.
Moreover, the Agreement provides: “This agreement contains the whole agreement between the Seller and Buyer and there are no other terms, obligations, covenants, representations, statements or conditions, oral or otherwise, of any kind whatsoever.” We note *635parenthetically, that this contention of plaintiffs would make this clause meaningless, and consequently such contention is devoid of merit: Bardwell v. The Willis Company, 375 Pa. 503, 508, 100 A. 2d 102.
It is difficult to understand, in view of the Parol Evidence Rule, how plaintiffs could be entitled to prove oral conversations or understandings which preceded the written agreement and thereby alter and vary the written Agreement as to one of the subjects provided for therein. To admit such evidence would make a mockery of the Parol Evidence Rule, as well as of the above mentioned clause of this Agreement.
Plaintiffs next contend that the evidence should have been admitted under the well established rule that parol evidence is admissible — not to vary, alter, contradict or add to, but — to aid in the interpretation of the language of a written contract whenever the language is ambiguous or not clear: Foulke v. Miller, 381 Pa. 587, 593, 112 A. 2d 124.
Defendant, on the other hand, contends that the written Agreement is clear and unambiguous and that the plaintiffs are in reality attempting to reform, alter and change the contract by substituting the words “only one office building” for the words “an office building”.
Plaintiffs’ contention is devoid of merit. There is no ambiguity in the written Agreement of Sale. Plaintiffs’ construction of the Agreement is erroneous and unjustifiable, and evidence of the alleged prior negotiations or understandings or oral agreements, flies in the teeth of the Parol Evidence Rule and was clearly inadmissible: Pellegrene v. Luther, 403 Pa. 212, 169 A. 2d 298; Bardwell v. The Willis Company, 375 Pa., supra; Caplan v. Saltzman, 407 Pa. 250, 180 A. 2d 240, and cases cited therein.
Decree affirmed; costs to be paid by appellants.
Italics, ours.
Real estate agent for buyer.