diff --git a/EKF/ekf.h b/EKF/ekf.h
index c75f6e4d23..272f85e29e 100644
--- a/EKF/ekf.h
+++ b/EKF/ekf.h
@@ -596,9 +596,13 @@ private:
 	// zero the specified range of columns in the state covariance matrix
 	void zeroCols(float (&cov_mat)[_k_num_states][_k_num_states], uint8_t first, uint8_t last);
 
-	// zero the specified range of off diagonals the state covariance matrix
+	// zero the specified range of off diagonals in the state covariance matrix
 	void zeroOffDiag(float (&cov_mat)[_k_num_states][_k_num_states], uint8_t first, uint8_t last);
 
+	// zero the specified range of off diagonals in the state covariance matrix
+	// set the diagonals to the supplied value
+	void setDiag(float (&cov_mat)[_k_num_states][_k_num_states], uint8_t first, uint8_t last, float variance);
+
 	// calculate the measurement variance for the optical flow sensor
 	float calcOptFlowMeasVar();
 
diff --git a/EKF/ekf_helper.cpp b/EKF/ekf_helper.cpp
index 6e4b372694..6b36b4fed6 100644
--- a/EKF/ekf_helper.cpp
+++ b/EKF/ekf_helper.cpp
@@ -1227,6 +1227,20 @@ void Ekf::zeroOffDiag(float (&cov_mat)[_k_num_states][_k_num_states], uint8_t fi
 
 }
 
+void Ekf::setDiag(float (&cov_mat)[_k_num_states][_k_num_states], uint8_t first, uint8_t last, float variance)
+{
+	// zero rows and columns
+	zeroRows(cov_mat, first, last);
+	zeroCols(cov_mat, first, last);
+
+	// set diagonals
+	uint8_t row;
+	for (row = first; row <= last; row++) {
+		cov_mat[row][row] = variance;
+	}
+
+}
+
 bool Ekf::global_position_is_valid()
 {
 	// return true if we are not doing unconstrained free inertial navigation and the origin is set