diff --git a/EKF/common.h b/EKF/common.h
index 28ec23a303..998c0c9493 100644
--- a/EKF/common.h
+++ b/EKF/common.h
@@ -243,6 +243,7 @@ struct parameters {
 	float wind_vel_p_noise_scaler{0.5f};	///< scaling of wind process noise with vertical velocity
 	float terrain_p_noise{5.0f};		///< process noise for terrain offset (m/sec)
 	float terrain_gradient{0.5f};		///< gradient of terrain used to estimate process noise due to changing position (m/m)
+	float terrain_timeout{10.f};		///< maximum time for invalid bottom distance measurements before resetting terrain estimate (s)
 
 	// initialization errors
 	float switch_on_gyro_bias{0.1f};	///< 1-sigma gyro bias uncertainty at switch on (rad/sec)
diff --git a/EKF/terrain_estimator.cpp b/EKF/terrain_estimator.cpp
index 380fe1ff6f..75fa5a84fc 100644
--- a/EKF/terrain_estimator.cpp
+++ b/EKF/terrain_estimator.cpp
@@ -166,7 +166,8 @@ void Ekf::fuseHagl()
 
 	} else {
 		// If we have been rejecting range data for too long, reset to measurement
-		if (isTimedOut(_time_last_hagl_fuse, (uint64_t)10E6)) {
+		const uint64_t timeout = static_cast<uint64_t>(_params.terrain_timeout * 1e6f);
+		if (isTimedOut(_time_last_hagl_fuse, timeout)) {
 			_terrain_vpos = _state.pos(2) + meas_hagl;
 			_terrain_var = obs_variance;