diff --git a/libraries/AP_AHRS/AP_AHRS_Backend.h b/libraries/AP_AHRS/AP_AHRS_Backend.h
index 66f261d7f5..0e42385b41 100644
--- a/libraries/AP_AHRS/AP_AHRS_Backend.h
+++ b/libraries/AP_AHRS/AP_AHRS_Backend.h
@@ -25,7 +25,6 @@
 #include <AP_Airspeed/AP_Airspeed.h>
 #include <AP_InertialSensor/AP_InertialSensor.h>
 
-class OpticalFlow;
 #define AP_AHRS_TRIM_LIMIT 10.0f        // maximum trim angle in degrees
 #define AP_AHRS_RP_P_MIN   0.05f        // minimum value for AHRS_RP_P parameter
 #define AP_AHRS_YAW_P_MIN  0.05f        // minimum value for AHRS_YAW_P parameter