Load-resonant inverters drive their loads at the load's resonant frequency. The frequency control unit of this type of inverter may be implemented simply by using phase-locked loop-based tuning circuits. However, a problem is detected that may arise randomly in this type of frequency control scheme. When this problem occurs, the inverter's frequency jumps to a value unrelated to the load-resonant frequency and sticks there. Following the analysis of the underlying cause of the problem, it is understood that the problem is caused by the two-valued characteristic of a phase frequency detector. A correction circuit is presented in this paper. When the proposed correction circuit was incorporated into the existing tuning circuitry, the problem was eliminated in the experiments. This shows not only that the correction circuit works well but also that the mechanism of the malfunction was diagnosed accurately.