diff --git a/libraries/AP_Proximity/AP_Proximity.cpp b/libraries/AP_Proximity/AP_Proximity.cpp
index 3ef0db827e..7587835e59 100644
--- a/libraries/AP_Proximity/AP_Proximity.cpp
+++ b/libraries/AP_Proximity/AP_Proximity.cpp
@@ -16,6 +16,7 @@
 #include "AP_Proximity.h"
 
 #if HAL_PROXIMITY_ENABLED
+#include "AP_Proximity_Backend.h"
 #include "AP_Proximity_RPLidarA2.h"
 #include "AP_Proximity_TeraRangerTower.h"
 #include "AP_Proximity_TeraRangerTowerEvo.h"