diff --git a/selfdrive/car/interfaces.py b/selfdrive/car/interfaces.py
index 528afdb9..f049434b 100644
--- a/selfdrive/car/interfaces.py
+++ b/selfdrive/car/interfaces.py
@@ -13,6 +13,9 @@ from selfdrive.controls.lib.vehicle_model import VehicleModel
 
 GearShifter = car.CarState.GearShifter
 EventName = car.CarEvent.EventName
+
+# WARNING: this value was determined based on the model's training distribution,
+#          model predictions above this speed can be unpredictable
 MAX_CTRL_SPEED = (V_CRUISE_MAX + 4) * CV.KPH_TO_MS  # 135 + 4 = 86 mph
 
 # generic car and radar interfaces