Copying dates in Excel

Hello,

I created a workbook in Excel and frequently need to copy the same date down a single column. I've always been able to simply grab the + in the bottom right corner of a cell and drag it down the column to copy the same date into each cell. I must have done something wrong setting up this new workbook. When I try to copy the date, using the same method, the column fills with a series of consecutive dates instead of simply copying the same vale into each cell. What do I need to do to fix this? I know the solution is simple, but I can't think of the correct wording to find the answer.

Thanks.