diff --git a/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp b/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
index 091c176a3a..911539f0dc 100644
--- a/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
+++ b/libraries/AP_AHRS/AP_AHRS_NavEKF.cpp
@@ -118,8 +118,11 @@ void AP_AHRS_NavEKF::update_EKF1(void)
             start_time_ms = AP_HAL::millis();
         }
         // slight extra delay on EKF1 to prioritise EKF2 for memory
-        if (AP_HAL::millis() - start_time_ms > startup_delay_ms + 100U) {
+        if (AP_HAL::millis() - start_time_ms > startup_delay_ms + 100U || force_ekf) {
             ekf1_started = EKF1.InitialiseFilterDynamic();
+            if (force_ekf) {
+                return;
+            }
         }
     }
     if (ekf1_started) {
@@ -189,8 +192,11 @@ void AP_AHRS_NavEKF::update_EKF2(void)
         if (start_time_ms == 0) {
             start_time_ms = AP_HAL::millis();
         }
-        if (AP_HAL::millis() - start_time_ms > startup_delay_ms) {
+        if (AP_HAL::millis() - start_time_ms > startup_delay_ms || force_ekf) {
             ekf2_started = EKF2.InitialiseFilter();
+            if (force_ekf) {
+                return;
+            }
         }
     }
     if (ekf2_started) {
diff --git a/libraries/AP_AHRS/AP_AHRS_NavEKF.h b/libraries/AP_AHRS/AP_AHRS_NavEKF.h
index 21115bc070..486e1c540c 100644
--- a/libraries/AP_AHRS/AP_AHRS_NavEKF.h
+++ b/libraries/AP_AHRS/AP_AHRS_NavEKF.h
@@ -217,6 +217,9 @@ public:
 
     bool getGpsGlitchStatus();
 
+    // used by Replay to force start at right timestamp
+    void force_ekf_start(void) { force_ekf = true; }
+    
 private:
     enum EKF_TYPE {EKF_TYPE_NONE=0,
 #if AP_AHRS_WITH_EKF1
@@ -235,8 +238,9 @@ private:
 
     NavEKF &EKF1;
     NavEKF2 &EKF2;
-    bool ekf1_started = false;
-    bool ekf2_started = false;
+    bool ekf1_started:1;
+    bool ekf2_started:1;
+    bool force_ekf:1;
     Matrix3f _dcm_matrix;
     Vector3f _dcm_attitude;
     Vector3f _gyro_bias;