A commercial GaAIAs diode laser is frequency locked to a Fabry-Perot interferometer. The temperature stabilization loop of this diode laser system maintains the relative frequency stability within 11 kHz. When the frequency control loop is closed, the relative frequency stability is improved to 450 Hz. A previously neglected frequency offset is also analyzed. This offset is a result of the injection current modulation technique commonly used to frequency lock diode lasers. The calculated frequency offset in our system is 150 kHz.