In a nonjury trial the court awarded Clifton Brock, a registered real estate broker, $67,500 as a commission in connectiqn with sale of a ranch for $675,000. Although Brock did not conclude the sale, the trial court found that he was the procuring cause and that the equitable owners of the property had agreed to pay him a ten percent commission if he effected a sale. See Fearick v. Smugglers Cove, Inc., 379 So.2d 400 (Fla.2d DCA 1980). Higgenbotham Realty, Inc., and Martin Higgenbotham contend the trial court erred in entering judgment for Brock. There was conflicting evidence; however, substantial competent evidence supports the trial court’s finding that Brock was the procuring cause of the sale. Appellants’ other contentions are without merit.

Brock cross-appeals the court’s failure to include prejudgment interest in its award. Since this was a contract action involving a liquidated sum, that is, ten percent of the sale price, the court should have awarded Brock prejudgment interest. Kennedy v. George Cully Real Estate, Inc., 336 So.2d 484 (Fla.3d DCA 1976). See Town of Longboat Key v. Carl E. Widell & Son, 362 So.2d 719 (Fla.2d DCA 1978).

Affirmed in part, reversed in part and remanded for entry of an amended judgment to include prejudgment interest.