diff --git a/matlab/mcmc_ifac.m b/matlab/mcmc_ifac.m
index bc7be30c43e2a0a9aa11e6234730b48b04985f5e..38ed34ee90d80c952e071ac9d170dde2a477876d 100644
--- a/matlab/mcmc_ifac.m
+++ b/matlab/mcmc_ifac.m
@@ -30,6 +30,9 @@ function Ifac = mcmc_ifac(X, Nc)
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
 Nc = min(Nc, length(X)/2);
+if mod(Nc,2),
+    Nc=Nc-1;
+end
 AcorrXSIM = autocorr(X(:), Nc);
 %
 %Calculate the Parzen Weight