diff --git a/libraries/AP_Gripper/AP_Gripper_Servo.h b/libraries/AP_Gripper/AP_Gripper_Servo.h
index 9b1161f70f..87636f02ed 100644
--- a/libraries/AP_Gripper/AP_Gripper_Servo.h
+++ b/libraries/AP_Gripper/AP_Gripper_Servo.h
@@ -37,7 +37,7 @@ public:
     bool released() const override;
 
     // valid - returns true if the backend should be working
-    bool valid() const;
+    bool valid() const override;
 
 protected: