diff --git a/matlab/+gtsam/covarianceEllipse.m b/matlab/+gtsam/covarianceEllipse.m
index 7728fc866..387d7cd12 100644
--- a/matlab/+gtsam/covarianceEllipse.m
+++ b/matlab/+gtsam/covarianceEllipse.m
@@ -1,16 +1,17 @@
-function covarianceEllipse(x,P,color)
+function covarianceEllipse(x,P,color, k)
 % covarianceEllipse plots a Gaussian as an uncertainty ellipse
 % Based on Maybeck Vol 1, page 366
 % k=2.296 corresponds to 1 std, 68.26% of all probability
 % k=11.82 corresponds to 3 std, 99.74% of all probability
 %
-% covarianceEllipse(x,P,color)
+% covarianceEllipse(x,P,color,k)
 % it is assumed x and y are the first two components of state x
+% k is scaling for std deviations, defaults to 1 std
 
 [e,s] = eig(P(1:2,1:2));
 s1 = s(1,1);
 s2 = s(2,2);
-k = 2.296;
+if nargin<4, k = 2.296; end;
 [ex,ey] = ellipse( sqrt(s1*k)*e(:,1), sqrt(s2*k)*e(:,2), x(1:2) );
 line(ex,ey,'color',color);