diff --git a/EKF/ekf.cpp b/EKF/ekf.cpp
index e15cb646a5..68d709483f 100644
--- a/EKF/ekf.cpp
+++ b/EKF/ekf.cpp
@@ -92,6 +92,7 @@ Ekf::Ekf():
 	_hgt_counter(0),
 	_rng_filt_state(0.0f),
 	_mag_counter(0),
+	_ev_counter(0),
 	_time_last_mag(0),
 	_hgt_sensor_offset(0.0f),
 	_terrain_vpos(0.0f),
@@ -387,7 +388,7 @@ bool Ekf::update()
 
 bool Ekf::initialiseFilter(void)
 {
-	// Keep accumulating measurements until we have a minimum of 10 samples for the baro and magnetoemter
+	// Keep accumulating measurements until we have a minimum of 10 samples for the required sensors
 
 	// Sum the IMU delta angle measurements
 	imuSample imu_init = _imu_buffer.get_newest();
@@ -406,6 +407,17 @@ bool Ekf::initialiseFilter(void)
 		}
 	}
 
+	// Count the number of external vision measurements received
+	if (_ext_vision_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_ev_sample_delayed)) {
+		if (_ev_counter == 0 && _ev_sample_delayed.time_us !=0) {
+			// initialise the counter
+			_ev_counter = 1;
+		} else if (_ev_counter != 0) {
+			// increment the sample count
+			_ev_counter ++;
+		}
+	}
+
 	// set the default height source from the adjustable parameter
 	if (_hgt_counter == 0) {
 		if (_params.fusion_mode & MASK_USE_EVPOS) {
@@ -454,7 +466,10 @@ bool Ekf::initialiseFilter(void)
 	}
 
 	// check to see if we have enough measurements and return false if not
-	if (_hgt_counter <= 10 || _mag_counter <= 10) {
+	bool hgt_count_fail = _hgt_counter <= 10;
+	bool mag_count_fail = _mag_counter <= 10;
+	bool ev_count_fail = ((_params.fusion_mode & MASK_USE_EVPOS) || (_params.fusion_mode & MASK_USE_EVYAW)) && (_ev_counter <= 10);
+	if (hgt_count_fail || mag_count_fail || ev_count_fail) {
 		return false;
 
 	} else {
diff --git a/EKF/ekf.h b/EKF/ekf.h
index 66691d5b46..55ffa5c363 100644
--- a/EKF/ekf.h
+++ b/EKF/ekf.h
@@ -209,9 +209,10 @@ private:
 	float _gps_alt_ref;		// WGS-84 height (m)
 
 	// Variables used to initialise the filter states
-	uint32_t _hgt_counter;		// number of height samples taken
+	uint32_t _hgt_counter;		// number of height samples read during initialisation
 	float _rng_filt_state;		// filtered height measurement
-	uint32_t _mag_counter;		// number of magnetometer samples taken
+	uint32_t _mag_counter;		// number of magnetometer samples read during initialisation
+	uint32_t _ev_counter;		// number of exgernal vision samples read during initialisation
 	uint64_t _time_last_mag;	// measurement time of last magnetomter sample
 	Vector3f _mag_filt_state;	// filtered magnetometer measurement
 	Vector3f _delVel_sum;		// summed delta velocity