diff --git a/demos/gtk-demo/main.c b/demos/gtk-demo/main.c
index f7ec23d236..c0259ad3a0 100644
--- a/demos/gtk-demo/main.c
+++ b/demos/gtk-demo/main.c
@@ -1056,8 +1056,6 @@ command_line (GApplication            *app,
 
   window = gtk_application_get_windows (GTK_APPLICATION (app))->data;
 
-  gtk_window_set_icon_name (GTK_WINDOW (window), "org.gtk.Demo4");
-
   if (name == NULL)
     goto out;
 
diff --git a/demos/node-editor/node-editor-application.c b/demos/node-editor/node-editor-application.c
index ec29941c9e..630807bde1 100644
--- a/demos/node-editor/node-editor-application.c
+++ b/demos/node-editor/node-editor-application.c
@@ -223,8 +223,6 @@ node_editor_application_activate (GApplication *app)
   if (g_strcmp0 (PROFILE, "devel") == 0)
     gtk_widget_add_css_class (GTK_WIDGET (win), "devel");
 
-  gtk_window_set_icon_name (GTK_WINDOW (win), "org.gtk.gtk4.NodeEditor");
-
   gtk_window_present (GTK_WINDOW (win));
 }
 
diff --git a/demos/print-editor/print-editor.c b/demos/print-editor/print-editor.c
index a438eeeec8..cfe528d582 100644
--- a/demos/print-editor/print-editor.c
+++ b/demos/print-editor/print-editor.c
@@ -788,7 +788,6 @@ activate (GApplication *app)
   if (g_strcmp0 (PROFILE, "devel") == 0)
     gtk_widget_add_css_class (GTK_WIDGET (main_window), "devel");
 
-  gtk_window_set_icon_name (GTK_WINDOW (main_window), "org.gtk.PrintEditor4");
   gtk_window_set_default_size (GTK_WINDOW (main_window), 400, 600);
   gtk_application_window_set_show_menubar (GTK_APPLICATION_WINDOW (main_window), TRUE);
   update_title (GTK_WINDOW (main_window));
diff --git a/demos/widget-factory/widget-factory.c b/demos/widget-factory/widget-factory.c
index 2f9a2d2fd1..4280b849cc 100644
--- a/demos/widget-factory/widget-factory.c
+++ b/demos/widget-factory/widget-factory.c
@@ -2232,7 +2232,6 @@ activate (GApplication *app)
   if (g_strcmp0 (PROFILE, "devel") == 0)
     gtk_widget_add_css_class (GTK_WIDGET (window), "devel");
 
-  gtk_window_set_icon_name (window, "org.gtk.WidgetFactory4");
   gtk_application_add_window (GTK_APPLICATION (app), window);
   g_action_map_add_action_entries (G_ACTION_MAP (window),
                                    win_entries, G_N_ELEMENTS (win_entries),
diff --git a/gtk/gtkapplication.c b/gtk/gtkapplication.c
index 17da2ed395..e065823910 100644
--- a/gtk/gtkapplication.c
+++ b/gtk/gtkapplication.c
@@ -88,6 +88,10 @@
  * displays the shortcuts window, associate the item with the action
  * `win.show-help-overlay`.
  *
+ * `GtkApplication` will also automatically set the application id as the
+ * default window icon. Use [func@Gtk.Window.set_default_icon_name] or
+ * [property@Gtk.Window:icon-name] to override that behavior.
+ *
  * ## A simple application
  *
  * [A simple example](https://gitlab.gnome.org/GNOME/gtk/tree/main/examples/bp/bloatpad.c)
@@ -244,6 +248,23 @@ gtk_application_load_resources (GtkApplication *application)
   }
 }
 
+static void
+gtk_application_set_window_icon (GtkApplication *application)
+{
+  GtkIconTheme *default_theme;
+  const char *appid;
+
+  if (gtk_window_get_default_icon_name () != NULL)
+    return;
+
+  default_theme = gtk_icon_theme_get_for_display (gdk_display_get_default ());
+  appid = g_application_get_application_id (G_APPLICATION (application));
+
+  if (!gtk_icon_theme_has_icon (default_theme, appid))
+    return;
+
+  gtk_window_set_default_icon_name (appid);
+}
 
 static void
 gtk_application_startup (GApplication *g_application)
@@ -267,6 +288,7 @@ gtk_application_startup (GApplication *g_application)
   gtk_application_impl_startup (priv->impl, priv->register_session);
 
   gtk_application_load_resources (application);
+  gtk_application_set_window_icon (application);
 
   gdk_profiler_end_mark (before, "Application startup", NULL);
 }