diff --git a/libraries/AP_AHRS/AP_AHRS.h b/libraries/AP_AHRS/AP_AHRS.h
index a4bd0c3979..3113003551 100644
--- a/libraries/AP_AHRS/AP_AHRS.h
+++ b/libraries/AP_AHRS/AP_AHRS.h
@@ -25,6 +25,7 @@
 
 #include <AP_HAL/Semaphores.h>
 
+#include "AP_AHRS_Backend.h"
 #include <AP_NavEKF2/AP_NavEKF2.h>
 #include <AP_NavEKF3/AP_NavEKF3.h>
 #include <AP_NavEKF/AP_Nav_Common.h>              // definitions shared by inertial and ekf nav filters