diff --git a/Mac/MainWindow/MainWindowController.swift b/Mac/MainWindow/MainWindowController.swift
index 4e51e3e40..f4cea74d9 100644
--- a/Mac/MainWindow/MainWindowController.swift
+++ b/Mac/MainWindow/MainWindowController.swift
@@ -17,7 +17,7 @@ enum TimelineSourceMode {
 	case regular, search
 }
 
-class MainWindowController : NSWindowController, NSUserInterfaceValidations {
+final class MainWindowController : NSWindowController, NSUserInterfaceValidations {
 
     @IBOutlet weak var articleThemePopUpButton: NSPopUpButton?