This cause is before us on appeal from an Okaloosa County Circuit Court summary denial of appellant’s Rule 3.850 motion for postconviction relief which sought to vacate the court’s retention of jurisdiction over one-third of two life sentences and one 300-year sentence. It is improper for the trial court to retain jurisdiction over a portion of a life sentence in this manner because it is impossible to calculate the length of time over which jurisdiction is retained. Stettler v. State, 475 So.2d 1009 (Fla. 1st DCA 1985). Accordingly, the court’s retention of jurisdiction over one-third of the two life sentences is vacated.