diff --git a/src/@dseries/backcast.m b/src/@dseries/backcast.m
index b26b0b943b97d58f15e42e1cd76ef2f98e92c14e..8dff9803057acef6076fa5b610ab10f251d16f48 100644
--- a/src/@dseries/backcast.m
+++ b/src/@dseries/backcast.m
@@ -31,7 +31,12 @@ function q = backcast(o, p, diff)  % --*-- Unitary tests --*--
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
 q = copy(o);
-q.backcast_(p);
+
+if nargin>2
+    q.backcast_(p, diff);
+else
+    q.backcast_(p);
+end
 
 return