diff --git a/matlab/set_default_option.m b/matlab/set_default_option.m
index 8b91d5e267461c9b77e9ae8f8b9c2055f2c9da63..43910ba296c9f07e8f94081567b693214d038f08 100644
--- a/matlab/set_default_option.m
+++ b/matlab/set_default_option.m
@@ -41,11 +41,11 @@ if isempty(options.(field))
     return
 end
 
-if ~iscell(options.(field))
+if ~iscell(options.(field)) && ~isdates(options.(field))
     if isnan(options.(field))
         options.(field) = default;
         return
     end
 end
 
-% 06/07/03 MJ added ; to eval expression
\ No newline at end of file
+% 06/07/03 MJ added ; to eval expression