diff --git a/include/camera/CameraHardwareInterface.h b/include/camera/CameraHardwareInterface.h
index 1529db7..6a66e3c 100644
--- a/include/camera/CameraHardwareInterface.h
+++ b/include/camera/CameraHardwareInterface.h
@@ -221,6 +221,7 @@
  */
 extern "C" int HAL_getNumberOfCameras();
 extern "C" void HAL_getCameraInfo(int cameraId, struct CameraInfo* cameraInfo);
+/* HAL should return NULL if it fails to open camera hardware. */
 extern "C" sp<CameraHardwareInterface> HAL_openCameraHardware(int cameraId);
 
 };  // namespace android