diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp b/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
index 59145351b7..e03947b2b5 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_core.cpp
@@ -409,6 +409,9 @@ bool NavEKF3_core::InitialiseFilterBootstrap(void)
 {
     // If we are a plane and don't have GPS lock then don't initialise
     if (assume_zero_sideslip() && AP::gps().status() < AP_GPS::GPS_OK_FIX_3D) {
+        hal.util->snprintf(prearm_fail_string,
+                    sizeof(prearm_fail_string),
+                    "EKF3 init failure: No GPS lock");
         statesInitialised = false;
         return false;
     }