
290 S.E.2d 387 (1982)
PROPST CONSTRUCTION CO.
v.
NORTH CAROLINA DEPARTMENT OF TRANSPORTATION.
No. 8119SC604.
Court of Appeals of North Carolina.
April 20, 1982.
*388 Kluttz, Hamlin, Reamer, Blankenship & Kluttz by Clarence Kluttz, and Malcolm Blankenship, Jr., Salisbury, for plaintiff-appellant.
Atty. Gen., Rufus L. Edmisten by Associate Atty. Gen., Blackwell M. Brogden, Jr., Raleigh, for the State.
BECTON, Judge.

Plaintiff's Appeal
Plaintiff assigns as error the trial court's granting of summary judgment in favor of defendant and its denial of partial summary judgment in favor of plaintiff. Four arguments are presented. For the reasons that follow, we believe the trial court erred in not submitting the case to the jury.
First, plaintiff contends that the doctrine of prevention relied upon by defendant in its motion for summary judgment was inappropriate under the facts of this case. The doctrine of prevention is that "one who prevents the performance of a condition, or makes it impossible by his own act, will not be permitted to take advantage of the nonperformance." Harwood v. Shoe, 141 N.C. 161, 163, 53 S.E. 616, 616 (1906). In order to excuse nonperformance, the conduct on the part of the party who allegedly prevented performance "`must be wrongful, and ... in excess of his legal rights.'" Goldston Brothers v. Newkirk, *389 233 N.C. 428, 432, 64 S.E.2d 424, 427 (1951), quoting Page on Contracts, Vol. 5, Sec. 2919, p. 5145. See also 6 Corbin on Contracts § 1264 (1962).
Defendant's contention, set forth in its motion for summary judgment, was that plaintiff, by failing to provide accurate weight scales, prevented defendant's performance of the contract and should, therefore, be estopped from taking advantage of its failure. From the documents considered on the motion for summary judgment, however, it appears that defendant's contention oversimplifies a more complex factual situation. When we view the evidence set forth in those documents in the light most favorable to the plaintiff, as must be done in ruling on a motion for summary judgment, Zimmerman v. Hogg & Allen, 286 N.C. 24, 29, 209 S.E.2d 795, 798 (1974), we find that it tended to show that plaintiff, in accordance with the contract, provided the scales for weighing the stones for the highway project; that, under the terms of the contract, defendant had the responsibility to check the scales prior to use; that there was a representative of defendant present at the scales, signing each weight ticket; that, at about the mid-point of the project, the superintendent of hauling (who worked for Dickerson, Inc.) informed defendant's representatives that something was wrong with the scales, "because the weight had... [fallen] off so much;" and that the DOT representative agreed that something appeared to be wrong.
When deposed, an employee of Piedmont Scale Service stated that he examined the scales on 22 August 1978, after the project was completed, and found them broken. The scales were "underweighing" the vehicles, and the heavier the true weight of the vehicle, the greater the degree of error. Although the contract between plaintiff and defendant did not establish which party had the continuing responsibility to check the scales, Dickerson's superintendent of hauling stated in his deposition that the State "has a man that comes around and checks the scales." Nowhere in defendant's motion and nowhere in the documents considered on the motion for summary judgment do we find any allegation or evidence that plaintiff caused the scales to malfunction.
After reviewing the foregoing evidence, this Court agrees with the plaintiff that the doctrine of prevention does not apply to the circumstances of this case. Again, it is not clear who, plaintiff or defendant, had the responsibility to check the accuracy of the scales. Based upon the deposition of Dickerson's superintendent of hauling, it appears that the defendant normally checked the accuracy of the scales. Under the evidence considered on defendant's motion for summary judgment, plaintiff cannot be said to have "prevented" defendant's performance under the contract, i.e. defendant's payment for the total amount of ABC delivered to the project.
Under the contract, defendant was obligated to pay for the actual tonnage of ABC delivered for the Highway 220 project. Defendant, however, paid only for the amount of ABC which showed on the allegedly defective scales. We believe that the evidence set forth at the hearing on the motions for summary judgment established a genuine issue of material fact as to how much ABC was actually delivered to the project. During the project, as the ABC was delivered to the stockpiles, plaintiff's employees had maintained records of tonnage used on the project by calculating an average weight per truck per day and multiplying that average by the number of trucks on the given day. The total figure they obtained was 177,334.25 tons. Compared with this is the estimate of 170,974 tons made by defendant in "cross-sectioning" the stockpiles. The stockpiles were under the control and supervision of defendant and were depleted at the end of the project. This evidence as well as the evidence derived from the weight tickets should have been allowed to go to the jury in order for the jury to determine the factual dispute concerning tonnage of ABC delivered. Summary judgment in favor of defendant was, therefore, improperly granted.
*390 Having determined that plaintiff should be allowed to present to the jury its evidence of breach of an express contract, we find that plaintiff's argument based on the theory of quantum meruit is inappropriate. "[Q]uantum meruit must rest in an implied contract," Burns v. Burns, 4 N.C. App. 426, 429, 167 S.E.2d 82, 84 (1969), and there can be no implied contract when there is an enforceable express contract between the parties as to the same subject matter. Elec-Trol, Inc. v. Contractors, Inc., 54 N.C. App. 626, 630, 284 S.E.2d 119, 121 (1981).
Furthermore, we reject plaintiff's argument that it was entitled to summary judgment on the issue of liability. It is for the jury to determine what amount of ABC was delivered to the project. The tonnage established by using the allegedly defective scales presents a genuine issue as to whether the defendant is liable for more tonnage than that for which it has paid.
Plaintiff's final argument is that the trial court erroneously entered judgment dismissing the complaint for failure to state a claim for relief under G.S. 1A-1, Rule 12(b)(6). In view of the trial court's language and the fact that, by consideration of matters outside the pleadings, defendant's motion to dismiss was converted to a motion for summary judgment under G.S. 1A-1, Rule 56, we have difficulty reading the judgment as allowing defendant's Rule 12(b)(6) motion. To the extent that it is so interpreted, it is erroneous.

Defendant's Cross-Assignments of Error
Under defendant's cross-assignments of error, it argues that the trial court erred in allowing oral testimony to be introduced into the record at the summary judgment hearing. While this Court has expressed some concern about the "overzealous use" of oral testimony in a hearing in a summary judgment motion, Walton v. Meir, 14 N.C.App. 183, 188-89, 188 S.E.2d 56, 60-61, cert. denied, 281 N.C. 515, 189 S.E.2d 35 (1972), the permissibility of such testimony was noted in Kessing v. Mortgage Corp., 278 N.C. 523, 180 S.E.2d 823 (1971), on the basis of G.S. 1A-1, Rule 43(e). Consequently, we find no error in the trial court's admission of oral testimony.
In conclusion, summary judgment granted in defendant's favor is
Reversed.
HEDRICK and HILL, JJ., concur.
