diff --git a/src/@dates/subperiod.m b/src/@dates/subperiod.m
index 0722b672291ff83b258315510e982103ea90f974..245b3617cfad07bdfd9eb0d735d14c146e90997a 100644
--- a/src/@dates/subperiod.m
+++ b/src/@dates/subperiod.m
@@ -1,8 +1,8 @@
 function s = subperiod(d)
 
-% Returns the subperiod (half-year, quarter, month or week depending on the frequency).
+% Returns the subperiod (half-year, quarter, or month depending on the frequency).
 
-% Copyright (C) 2016-2020 Dynare Team
+% Copyright © 2016-2020 Dynare Team
 %
 % This code is free software: you can redistribute it and/or modify
 % it under the terms of the GNU General Public License as published by
@@ -17,4 +17,8 @@ function s = subperiod(d)
 % You should have received a copy of the GNU General Public License
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
+if freq==365 || freq==1
+    error('Method not available for daily or annual frequencies.')
+end
+
 s = d.time(2);
\ No newline at end of file