ActiveX control checkbox to (un-)check all checkboxes

Sub CheckAll()
    Dim lngIndex As Long
    Dim blnState As Boolean
    
    blnState = ActiveSheet.Shapes("CheckBox7").OLEFormat.Object.Object.Value
    For lngIndex = 1 To 6
        With ActiveSheet
            With .Shapes("CheckBox" & lngIndex)
                .OLEFormat.Object.Object.Value = blnState
            End With
        End With
    Next
    
End Sub