save .xlsx from active sheet, with sheet name, same address of current workbook

I try to save a new file .xlsx with the name of the worksheet, it works with .xls but I needed in a new version. Txs

The code I'm using is:

Sub save_active ()
'when I change it to ".xlsx" It doesnt work
'display the msg "file is corrupted"
MName = ActiveSheet.Name & ".xls"
MDir = ActiveWorkbook.Path
ActiveWorkbook.SaveAs Filename:=MDir & "\" & MName

End Sub