diff --git a/libraries/AP_AHRS/examples/AHRS_Test/AHRS_Test.pde b/libraries/AP_AHRS/examples/AHRS_Test/AHRS_Test.pde
index 79c862c8bc..e66e13e1be 100644
--- a/libraries/AP_AHRS/examples/AHRS_Test/AHRS_Test.pde
+++ b/libraries/AP_AHRS/examples/AHRS_Test/AHRS_Test.pde
@@ -21,6 +21,7 @@
 #include <AP_Compass.h>
 #include <AP_Airspeed.h>
 #include <AP_Baro.h>
+#include <AP_Semaphore.h>
 #include <DataFlash.h>
 #include <APM_RC.h>
 #include <GCS_MAVLink.h>