Laser diode injection-locking is a commonly used method to amplify laser light, while preserving its spectral properties. Fluctuations in the environmental conditions can cause injection-locking to fail, especially when operating with low seed powers or with a swept seed frequency. We present a method inspired by the Hänsch-Couillaud scheme to monitor and actively stabilize the conditions required for injection-locking a laser diode. Using only a few optical components, our scheme can run continuously in the background and is modulation-free. We demonstrate its efficacy by showing its robustness to large fluctuations in diode temperature, seed frequency and power, effectively extending the reliable operating range and stability over time.