diff --git a/EKF/ekf_helper.cpp b/EKF/ekf_helper.cpp
index 12ec0a9d2e..5f22cdf25a 100644
--- a/EKF/ekf_helper.cpp
+++ b/EKF/ekf_helper.cpp
@@ -42,6 +42,8 @@
 #include "ekf.h"
 #include "mathlib.h"
 
+using std::abs;
+
 // Reset the velocity states. If we have a recent and valid
 // gps measurement then use for velocity initialisation
 bool Ekf::resetVelocity()