diff --git a/EKF/ekf_helper.cpp b/EKF/ekf_helper.cpp
index 0f6ae7aa94..75db55cf99 100644
--- a/EKF/ekf_helper.cpp
+++ b/EKF/ekf_helper.cpp
@@ -868,7 +868,7 @@ Vector3f EstimatorInterface::cross_product(const Vector3f &vecIn1, const Vector3
 }
 
 // calculate the inverse rotation matrix from a quaternion rotation
-Matrix3f EstimatorInterface::quat_to_invrotmat(const Quaternion quat)
+Matrix3f EstimatorInterface::quat_to_invrotmat(const Quaternion& quat)
 {
 	float q00 = quat(0) * quat(0);
 	float q11 = quat(1) * quat(1);
diff --git a/EKF/estimator_interface.h b/EKF/estimator_interface.h
index 7d1c2b974e..9c78499816 100644
--- a/EKF/estimator_interface.h
+++ b/EKF/estimator_interface.h
@@ -380,6 +380,6 @@ protected:
 	Vector3f cross_product(const Vector3f &vecIn1, const Vector3f &vecIn2);
 
 	// calculate the inverse rotation matrix from a quaternion rotation
-	Matrix3f quat_to_invrotmat(const Quaternion quat);
+	Matrix3f quat_to_invrotmat(const Quaternion& quat);
 
 };