SaveAs works unless user selects file in SaveAsDialog - excel

Question

I'm using the code below so users can "export" the Workbook they're working on. Basically, they're working in a Read-only master workbook, when they click the sub below it executes a SaveAs to a folder the user selects with the file name of whatever is in: Sheets("Master").Range("B5")
This works fine, the only problem is that if there's a '.xlsm' file in the folder the user selects and they click it to grab the filename, the saved Workbook name becomes "XXXXXX.xlsm.xlsm". If the user doesn't click anything and hits save it works fine.
Any ideas? Let me know if this wasn't clear
Sub ExportTrip()
Dim ActSheet As Worksheet
Dim ActBook As Workbook
Dim CurrentFile As String
Dim NewFile As String
Application.ScreenUpdating = False ' Prevents screen refreshing.
CurrentFile = ThisWorkbook.FullName
NewFile = Application.GetSaveAsFilename( _
InitialFileName:=Sheets("Master").Range("B5"))
If NewFile <> "" And NewFile <> "False" Then
ActiveWorkbook.SaveAs filename:=NewFile & "xlsm", _
FileFormat:=52, _
Password:="", _
WriteResPassword:="", _
ReadOnlyRecommended:=False, _
CreateBackup:=False
Set ActBook = ActiveWorkbook
Workbooks.Open CurrentFile
Application.DisplayAlerts = False
ActBook.Close
Application.DisplayAlerts = True
End If
Application.ScreenUpdating = True
End Sub

Answer 1

Figured it out, needed to add file filter. See below:
Sub ExportTrip()
Dim ActSheet As Worksheet
Dim ActBook As Workbook
Dim CurrentFile As String
Dim NewFile As String
Application.ScreenUpdating = False ' Prevents screen refreshing.
CurrentFile = ThisWorkbook.FullName ' saves filename of current workbook
NewFile = Application.GetSaveAsFilename( _
InitialFileName:=Sheets("Master").Range("B5"), _
FileFilter:="ARMS Export *.xlsm (*.xlsm),") ' gets filename for exported workbook
If NewFile <> "" And NewFile <> "False" Then 'if user doesn't pick name
ActiveWorkbook.SaveAs filename:=NewFile, _
FileFormat:=52, _
Password:="", _
WriteResPassword:="", _
ReadOnlyRecommended:=False, _
CreateBackup:=False
Set ActBook = ActiveWorkbook 'declares variable for open workbook
Workbooks.Open CurrentFile 'reopens original workbook
Application.DisplayAlerts = False
ActBook.Close 'closes exported workbook
Application.DisplayAlerts = True
End If
Application.ScreenUpdating = True
End Sub