[otrs] how do I prevent the character set warning from showing

I see this warning when viewing messages sent from the ticket tracker [ The following text is in the "iso-8859-15" character set. ] [ Your display is set for the "ISO-8859-1" character set. ] [ Some special characters may be displayed incorrectly. ] What do I have to do to make it so that this does not show up. I am using otrs 1.3.1 --