Reversed and remanded for a new trial. We agree with appellant that the trial court erred in allowing a witness to be called as a court witness in violation of the rule set out in Jackson v. State, 498 So.2d 906 (Fla. 1986). Because it is clear from the record that the state relied heavily on the disputed prior statements made by this witness to prove its case against the appellant, we cannot conclude that the error was harmless. See State v. DiGuilio, 491 So.2d 1129 (Fla. 1986).