diff --git a/EKF/ekf_helper.cpp b/EKF/ekf_helper.cpp
index f86ca38be3..e4b0bc9b42 100644
--- a/EKF/ekf_helper.cpp
+++ b/EKF/ekf_helper.cpp
@@ -1596,6 +1596,7 @@ void Ekf::calcExtVisRotMat()
 	// calculate the quaternion delta between the EV and EKF reference frames at the EKF fusion time horizon
 	Quatf q_error = _state.quat_nominal * _ev_sample_delayed.quat.inversed();
 	q_error.normalize();
+	q_error.canonicalize();
 
 	// convert to a delta angle and apply a spike and low pass filter
 	Vector3f rot_vec = q_error.to_axis_angle();
@@ -1623,6 +1624,7 @@ void Ekf::calcExtVisRotMat()
 	// convert filtered vector to a quaternion and then to a rotation matrix
 	q_error.from_axis_angle(_ev_rot_vec_filt);
 	q_error.normalize();
+	q_error.canonicalize();
 	_ev_rot_mat = Dcmf(q_error); // rotation from EV reference to EKF reference
 
 }