diff --git a/EKF/ekf.cpp b/EKF/ekf.cpp
index b2c7ced31c..6ca20cb017 100644
--- a/EKF/ekf.cpp
+++ b/EKF/ekf.cpp
@@ -223,6 +223,7 @@ bool Ekf::initialiseFilter()
 	_time_last_delpos_fuse = _time_last_imu;
 	_time_last_hor_vel_fuse = _time_last_imu;
 	_time_last_hagl_fuse = _time_last_imu;
+	_time_last_flow_terrain_fuse = _time_last_imu;
 	_time_last_of_fuse = _time_last_imu;
 
 	// reset the output predictor state history to match the EKF initial values
diff --git a/EKF/ekf.h b/EKF/ekf.h
index 35136f5433..d5cbab5007 100644
--- a/EKF/ekf.h
+++ b/EKF/ekf.h
@@ -351,6 +351,7 @@ private:
 	uint64_t _time_last_ver_vel_fuse{0};	///< time the last fusion of verticalvelocity measurements was performed (uSec)
 	uint64_t _time_last_delpos_fuse{0};	///< time the last fusion of incremental horizontal position measurements was performed (uSec)
 	uint64_t _time_last_of_fuse{0};		///< time the last fusion of optical flow measurements were performed (uSec)
+	uint64_t _time_last_flow_terrain_fuse{0}; ///< time the last fusion of optical flow measurements for terrain estimation were performed (uSec)
 	uint64_t _time_last_arsp_fuse{0};	///< time the last fusion of airspeed measurements were performed (uSec)
 	uint64_t _time_last_beta_fuse{0};	///< time the last fusion of synthetic sideslip measurements were performed (uSec)
 	uint64_t _time_last_fake_pos{0};	///< last time we faked position measurements to constrain tilt errors during operation without external aiding (uSec)
diff --git a/EKF/terrain_estimator.cpp b/EKF/terrain_estimator.cpp
index 77cc681810..380fe1ff6f 100644
--- a/EKF/terrain_estimator.cpp
+++ b/EKF/terrain_estimator.cpp
@@ -244,7 +244,7 @@ void Ekf::fuseFlowForTerrain()
 		_terrain_vpos += Kx * _flow_innov(0);
 		// guard against negative variance
 		_terrain_var = fmaxf(_terrain_var - KxHxP, 0.0f);
-		_time_last_of_fuse = _time_last_imu;
+		_time_last_flow_terrain_fuse = _time_last_imu;
 	}
 
 	// Calculate observation matrix for flow around the vehicle y axis
@@ -272,7 +272,7 @@ void Ekf::fuseFlowForTerrain()
 		_terrain_vpos += Ky * _flow_innov(1);
 		// guard against negative variance
 		_terrain_var = fmaxf(_terrain_var - KyHyP, 0.0f);
-		_time_last_of_fuse = _time_last_imu;
+		_time_last_flow_terrain_fuse = _time_last_imu;
 	}
 }
 
@@ -283,8 +283,7 @@ void Ekf::updateTerrainValidity()
 
 	// we have been fusing optical flow measurements for terrain estimation within the last 5 seconds
 	// this can only be the case if the main filter does not fuse optical flow
-	const bool recent_flow_for_terrain_fusion = isRecent(_time_last_of_fuse, (uint64_t)5e6)
-						    && !_control_status.flags.opt_flow;
+	const bool recent_flow_for_terrain_fusion = isRecent(_time_last_flow_terrain_fuse, (uint64_t)5e6);
 
 	_hagl_valid = (_terrain_initialised && (recent_range_fusion || recent_flow_for_terrain_fusion));