Save Changes Window

I am trying to write an excel macro where I check to see if the data in cetain fields in numeric. If it is not, I replace that data with a zero. However, when I run the macro, a window pops up asking me if I want to save th changes I made to that spreadsheet. I do want to save these changes, but I don't want this message to appear. Is there a way to automate that process so I don't have to click "yes" everytime the program runs? My code is as follows:

For Each n In Worksheets("Manual").Range("M9:M29")
If Not IsNumeric(n) Then
n.Value = 0
End If
Next n