--- a/src/DefaultTimeline.vala	2020-05-23 23:55:51.509903993 +0200
+++ a/src/DefaultTimeline.vala	2020-05-23 23:58:06.929903012 +0200
@@ -47,7 +47,7 @@ 
   private double last_value = 0.0;
 
 
-  public DefaultTimeline (int id) {
+  protected DefaultTimeline (int id) {
     this.id = id;
     this.hscrollbar_policy = Gtk.PolicyType.NEVER;
     this.scrolled_to_start.connect (handle_scrolled_to_start);
--- a/src/MainWindow.vala	2020-05-24 00:02:22.109901164 +0200
+++ a/src/MainWindow.vala	2020-05-24 00:03:41.669900587 +0200
@@ -435,7 +435,7 @@ 
     if (account == null)
       return Gdk.EVENT_PROPAGATE;
 
-    unowned GLib.List<weak Gtk.Window> ws = this.application.get_windows ();
+    unowned GLib.List<Gtk.Window> ws = this.application.get_windows ();
     debug("Windows: %u", ws.length ());
 
     string[] startup_accounts = Settings.get ().get_strv ("startup-accounts");
--- a/src/Corebird.vala	2020-05-24 00:04:01.599900443 +0200
+++ a/src/Corebird.vala	2020-05-24 00:04:45.219900127 +0200
@@ -396,7 +396,7 @@ 
    */
   public bool is_window_open_for_screen_name (string screen_name,
                                               out MainWindow? window = null) {
-    unowned GLib.List<weak Gtk.Window> windows = this.get_windows ();
+    unowned GLib.List<Gtk.Window> windows = this.get_windows ();
     foreach (Gtk.Window win in windows) {
       if (win is MainWindow) {
         if (((MainWindow)win).account.screen_name == screen_name) {
@@ -411,7 +411,7 @@ 
 
   public bool is_window_open_for_user_id (int64 user_id,
                                           out MainWindow? window = null) {
-    unowned GLib.List<weak Gtk.Window> windows = this.get_windows ();
+    unowned GLib.List<Gtk.Window> windows = this.get_windows ();
     foreach (Gtk.Window win in windows) {
       if (win is MainWindow) {
         if (((MainWindow)win).account.id == user_id) {
@@ -428,7 +428,7 @@ 
    * Quits the application, saving all open windows and their geometries.
    */
   private void quit_application () {
-    unowned GLib.List<weak Gtk.Window> windows = this.get_windows ();
+    unowned GLib.List<Gtk.Window> windows = this.get_windows ();
     string[] startup_accounts = Settings.get ().get_strv ("startup-accounts");
     if (startup_accounts.length == 1 && startup_accounts[0] == "")
       startup_accounts.resize (0);