diff --git a/src/video/cocoa/cocoa_v.mm b/src/video/cocoa/cocoa_v.mm
--- a/src/video/cocoa/cocoa_v.mm
+++ b/src/video/cocoa/cocoa_v.mm
@@ -200,6 +200,8 @@ const char *VideoDriver_Cocoa::Start(con
 	/* Don't create a window or enter fullscreen if we're just going to show a dialog. */
 	if (!CocoaSetupApplication()) return NULL;
 
+	this->UpdateAutoResolution();
+
 	this->orig_res = _cur_resolution;
 	int width  = _cur_resolution.width;
 	int height = _cur_resolution.height;
@@ -303,6 +305,15 @@ void VideoDriver_Cocoa::EditBoxLostFocus
 }
 
 /**
+ * Get the resolution of the main screen.
+ */
+Dimension VideoDriver_Cocoa::GetScreenSize() const
+{
+	NSRect frame = [ [ NSScreen mainScreen ] frame ];
+	return { static_cast<uint>(NSWidth(frame)), static_cast<uint>(NSHeight(frame)) };
+}
+
+/**
  * Handle a change of the display area.
  */
 void VideoDriver_Cocoa::GameSizeChanged()