diff --git a/libraries/AP_NavEKF/EKF_Buffer.cpp b/libraries/AP_NavEKF/EKF_Buffer.cpp
index 928a8d655a..8474ccecf4 100644
--- a/libraries/AP_NavEKF/EKF_Buffer.cpp
+++ b/libraries/AP_NavEKF/EKF_Buffer.cpp
@@ -137,6 +137,7 @@ bool ekf_imu_buffer::init(uint32_t size)
     _size = size;
     _youngest = 0;
     _oldest = 0;
+    _filled = 0;
     return true;
 }