diff --git a/matlab/utilities/dates/isfreq.m b/matlab/utilities/dates/isfreq.m
index 38a779f20..79ba42c53 100644
--- a/matlab/utilities/dates/isfreq.m
+++ b/matlab/utilities/dates/isfreq.m
@@ -25,4 +25,15 @@ function B = isfreq(A)
 % You should have received a copy of the GNU General Public License
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
-B = (ischar(A) && ismember(upper(A),{'Y','A','Q','M','W'})) || ismember(A,[1 4 12 52]);
\ No newline at end of file
+B = 0;
+
+if ischar(A)
+    if isequal(length(A),1) && ismember(upper(A),{'Y','A','Q','M','W'})
+        B = 1;
+        return
+    end
+end
+
+if isnumeric(A) && isequal(length(A),1) && ismember(A,[1 4 12 52])
+    B = 1;
+end
\ No newline at end of file