diff --git a/libraries/AP_NavEKF3/AP_NavEKF3.h b/libraries/AP_NavEKF3/AP_NavEKF3.h
index 67ea03c597..e0f7cb4837 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3.h
+++ b/libraries/AP_NavEKF3/AP_NavEKF3.h
@@ -529,6 +529,7 @@ private:
     const uint16_t fusionTimeStep_ms = 10;         // The minimum time interval between covariance predictions and measurement fusions in msec
     const uint8_t sensorIntervalMin_ms = 50;       // The minimum allowed time between measurements from any non-IMU sensor (msec)
     const uint8_t flowIntervalMin_ms = 20;         // The minimum allowed time between measurements from optical flow sensors (msec)
+    const uint8_t extNavIntervalMin_ms = 20;       // The minimum allowed time between measurements from external navigation sensors (msec)
 
     struct {
         bool enabled:1;
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp
index 34a8702c12..33b1f7974c 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp
@@ -947,7 +947,7 @@ void NavEKF3_core::writeExtNavData(const Vector3f &pos, const Quaternion &quat,
 {
     // limit update rate to maximum allowed by sensor buffers and fusion process
     // don't try to write to buffer until the filter has been initialised
-    if (((timeStamp_ms - extNavMeasTime_ms) < 70) || !statesInitialised) {
+    if (((timeStamp_ms - extNavMeasTime_ms) < frontend->extNavIntervalMin_ms) || !statesInitialised) {
         return;
     } else {
         extNavMeasTime_ms = timeStamp_ms;
@@ -990,7 +990,7 @@ void NavEKF3_core::writeExtNavData(const Vector3f &pos, const Quaternion &quat,
 
 void NavEKF3_core::writeExtNavVelData(const Vector3f &vel, float err, uint32_t timeStamp_ms, uint16_t delay_ms)
 {
-    if ((timeStamp_ms - extNavVelMeasTime_ms) < 70) {
+    if ((timeStamp_ms - extNavVelMeasTime_ms) < frontend->extNavIntervalMin_ms) {
         return;
     }
 
diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
index cd042e3b0f..20531c4603 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
@@ -108,6 +108,12 @@ bool NavEKF3_core::setup_core(uint8_t _imu_index, uint8_t _core_index)
     // calculate buffer size for optical flow data
     const uint8_t flow_buffer_length = MIN((ekf_delay_ms / frontend->flowIntervalMin_ms) + 1, imu_buffer_length);
 
+    // calculate buffer size for external nav data
+    const uint8_t extnav_buffer_length = MIN((ekf_delay_ms / frontend->extNavIntervalMin_ms) + 1, imu_buffer_length);
+
+    // buffer size for external yaw
+    const uint8_t yaw_angle_buffer_length = MAX(obs_buffer_length, extnav_buffer_length);
+
     if(!storedGPS.init(obs_buffer_length)) {
         return false;
     }
@@ -129,7 +135,7 @@ bool NavEKF3_core::setup_core(uint8_t _imu_index, uint8_t _core_index)
     if(!storedWheelOdm.init(imu_buffer_length)) { // initialise to same length of IMU to allow for multiple wheel sensors
         return false;
     }
-    if(!storedYawAng.init(obs_buffer_length)) {
+    if(!storedYawAng.init(yaw_angle_buffer_length)) {
         return false;
     }
     // Note: the use of dual range finders potentially doubles the amount of data to be stored
@@ -140,10 +146,10 @@ bool NavEKF3_core::setup_core(uint8_t _imu_index, uint8_t _core_index)
     if(!storedRangeBeacon.init(imu_buffer_length)) {
         return false;
     }
-    if (!storedExtNav.init(obs_buffer_length)) {
+    if (!storedExtNav.init(extnav_buffer_length)) {
         return false;
     }
-    if (!storedExtNavVel.init(obs_buffer_length)) {
+    if (!storedExtNavVel.init(extnav_buffer_length)) {
         return false;
     }
     if(!storedIMU.init(imu_buffer_length)) {