Using Dir() To Select .xls But NOT .xlsx Files

Using Excel 2007:

I am trying to use dir() in a While...wend to get a specific list of files to process, but I want the list to only include those with a .xls extension, not those ending in .xlsx. It seems that the file filter ".xls" doesn't exclude those files with a ".xlsx" extension.

Sample code demonstrating the problem (will show the problem if there is at least one cycle that meets a*.xls and one that meets a*.xlsx).

Is there a workaround to this at the dir() level? Or do I need to go ahead and open the file and test its contents?

Sub TestDir()
On Error GoTo Nofile 'trap cancel, X-out of the dialog, etc.
With Application.FileDialog(msoFileDialogOpen)
.AllowMultiSelect = False
.InitialFileName = "a*.xls"
.Show
GetDir = .SelectedItems(1)
End With
On Error GoTo 0 'reset error handler