diff --git a/PID.h b/PID.h
index bf6b885..4ecfe64 100644
--- a/PID.h
+++ b/PID.h
@@ -6,7 +6,7 @@ typedef struct {
 	/* Controller gains */
 	float Kp;
 	float Ki;
-	float Kd;
+	float Kd; /* Note: since using derivative-on-measurement, Kd needs to be negative (in contrast to conventional 'derivative-on'error') */
 
 	/* Derivative low-pass filter time constant */
 	float tau;
diff --git a/PID_Test.c b/PID_Test.c
index 5d20da9..042b8d8 100644
--- a/PID_Test.c
+++ b/PID_Test.c
@@ -24,7 +24,7 @@ float TestSystem_Update(float inp);
 int main()
 {
     /* Initialise PID controller */
-    PIDController pid = { PID_KP, PID_KI, PID_KD,
+    PIDController pid = { PID_KP, PID_KI, -PID_KD,
                           PID_TAU,
                           PID_LIM_MIN, PID_LIM_MAX,
                           SAMPLE_TIME_S };