diff --git a/robust/mult_uncertainty.m b/robust/mult_uncertainty.m
index 4494af3..b5e565b 100644
--- a/robust/mult_uncertainty.m
+++ b/robust/mult_uncertainty.m
@@ -37,7 +37,10 @@ opt = wcOptions('MussvOptions','m3'); % for better lower bound
 resp_im = info_num.Bounds(:, 2) ./ info_den.Bounds(:, 1);
 
 data_2 = frd(resp_im, w);
-I_m_analytic_2 = tf(fitmagfrd(data_2, 2));
+% constrain the uncertainty to stay above the magnitude data
+Constraint.LowerBound = data_2;
+Constraint.UpperBound = [];
+I_m_analytic_2 = tf(fitmagfrd(data_2, 2, [], [], Constraint));
 
 sigma(I_m, w); hold;
 semilogx(w, 20*log10(info.Bounds(:, 2)), 'green');