diff --git a/matlab/set_default_option.m b/matlab/set_default_option.m
index 44976a15a1d2e286b7bc70a8a0cf26d3366bf346..371025008467de52d71997774da8b3b41305ca75 100644
--- a/matlab/set_default_option.m
+++ b/matlab/set_default_option.m
@@ -41,9 +41,13 @@ if isempty(options.(field))
     return
 end
 
+if isdates(options.(field))
+    return
+end
+
 if isnan(options.(field))
     options.(field) = default;
     return
 end
 
-% 06/07/03 MJ added ; to eval expression
\ No newline at end of file
+% 06/07/03 MJ added ; to eval expression