diff --git a/apps/vectorcraft/src/main.rs b/apps/vectorcraft/src/main.rs
index 8019276ec..112c71370 100644
--- a/apps/vectorcraft/src/main.rs
+++ b/apps/vectorcraft/src/main.rs
@@ -467,6 +467,7 @@ fn main() -> std::process::ExitCode {
                     rs.device.set_device_lost_callback(move |reason, msg| loss.report(&ctx, format!("{reason:?}: {msg}")));
                 }
                 app.custom_titlebar = custom_titlebar;
+                app.desktop_frame = !custom_titlebar;
                 if let Some(port) = control_port {
                     let rx = control_server::start(port, cc.egui_ctx.clone());
                     app = app.with_control(rx).with_automation_roots(roots.clone());
diff --git a/crates/ui-egui/src/app.rs b/crates/ui-egui/src/app.rs
index a74582972..61057acb1 100644
--- a/crates/ui-egui/src/app.rs
+++ b/crates/ui-egui/src/app.rs
@@ -123,6 +123,7 @@ impl VectorcraftApp {
             canvas_rect: None,
             hover_doc: None,
             custom_titlebar: false,
+            desktop_frame: false,
             last_window_title: String::new(),
             fullscreen_for_mode: false,
             graphics_adapter: None,
diff --git a/crates/ui-egui/src/chrome.rs b/crates/ui-egui/src/chrome.rs
index ae8fbccc0..135958756 100644
--- a/crates/ui-egui/src/chrome.rs
+++ b/crates/ui-egui/src/chrome.rs
@@ -129,13 +129,15 @@ pub fn app_bar(app: &mut VectorcraftApp, ui: &mut Ui) {
     }
 }
 
-/// Whether the window shows the system's title bar instead of the app drawing its own: Windows
-/// and Linux with Preferences › User Interface › System Title Bar. macOS always has system
-/// decorations, but keeps the in-app brand mark, so it never counts as system mode here; nor
-/// does the web build (the browser tab has no document title), nor an embedder that never
-/// turned the preference on.
+/// Whether the window shows the system's title bar instead of the app drawing its own
+/// ([`VectorcraftApp::desktop_frame`]): Windows with Preferences › User Interface › System Title
+/// Bar, and Linux whenever the desktop draws the frame, with or without the preference. The
+/// preference is read when the app starts, so changing it later does not change this. macOS
+/// always has system decorations, but keeps the in-app brand mark, so it never counts as system
+/// mode here; nor does the web build (the browser tab has no document title), nor an embedder
+/// without a window of its own.
 pub fn system_title_bar(app: &VectorcraftApp) -> bool {
-    !app.custom_titlebar && app.session.prefs.system_title_bar && !cfg!(any(target_os = "macos", target_arch = "wasm32"))
+    app.desktop_frame && !app.custom_titlebar && !cfg!(any(target_os = "macos", target_arch = "wasm32"))
 }
 
 /// The OS window title: the active document's name suffixed with the app name (a `*` prefix
diff --git a/crates/ui-egui/src/chrome/tests.rs b/crates/ui-egui/src/chrome/tests.rs
index 00d790964..55650c46e 100644
--- a/crates/ui-egui/src/chrome/tests.rs
+++ b/crates/ui-egui/src/chrome/tests.rs
@@ -1230,16 +1230,51 @@ fn the_zoom_hint_follows_animated_zoom() {
 fn title_test_app(custom_titlebar: bool) -> crate::VectorcraftApp {
     let mut app = crate::VectorcraftApp::new(Session::new(), Default::default());
     app.custom_titlebar = custom_titlebar;
+    app.desktop_frame = !custom_titlebar;
     // The preference that makes the shell launch without its own title bar.
     app.run("prefs.set", json!({"key": "systemTitleBar", "value": !custom_titlebar})).unwrap();
     app
 }
 
+/// How many brand marks one frame of the app bar paints.
+fn brand_marks(app: &mut crate::VectorcraftApp) -> usize {
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| super::app_bar(app, ui));
+    out.textures_delta.clear();
+    out.shapes.iter().filter(|c| matches!(&c.shape, egui::Shape::Mesh(m) if m.texture_id == crate::brand::texture_id(&ctx))).count()
+}
+
 #[test]
 fn without_the_preference_the_mark_stays() {
     // The default (e.g. the web build): no custom bar, no preference.
     let app = crate::VectorcraftApp::new(Session::new(), Default::default());
     assert!(!super::system_title_bar(&app));
+    // An embedder without a window of its own keeps the mark with the preference on too.
+    let mut app = crate::VectorcraftApp::new(Session::new(), Default::default());
+    app.run("prefs.set", json!({"key": "systemTitleBar", "value": true})).unwrap();
+    assert!(!super::system_title_bar(&app));
+    assert_eq!(brand_marks(&mut app), 1);
+}
+
+#[test]
+fn a_desktop_frame_hides_the_mark_whatever_the_preference_says() {
+    // Linux on a desktop that draws the frame (KDE, X11): the window has the desktop's title bar
+    // with System Title Bar off.
+    let mut app = crate::VectorcraftApp::new(Session::new(), Default::default());
+    app.desktop_frame = true;
+    app.run("prefs.set", json!({"key": "systemTitleBar", "value": false})).unwrap();
+    let hidden = !cfg!(target_os = "macos");
+    assert_eq!(super::system_title_bar(&app), hidden);
+    assert_eq!(brand_marks(&mut app), if hidden { 0 } else { 1 });
+    // The preference applies at the next start: changing it now leaves the window's frame, and the mark, as they are.
+    let mut app = title_test_app(false);
+    app.run("prefs.set", json!({"key": "systemTitleBar", "value": false})).unwrap();
+    assert_eq!(super::system_title_bar(&app), hidden);
+    let mut app = title_test_app(true);
+    app.run("prefs.set", json!({"key": "systemTitleBar", "value": true})).unwrap();
+    assert!(!super::system_title_bar(&app));
+    assert_eq!(brand_marks(&mut app), 1);
 }
 
 #[test]
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index fb8912455..9b054a683 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -198,6 +198,10 @@ pub struct VectorcraftApp {
     /// Windows and Linux: the window has no OS decorations, so the app bar is the title bar (drag,
     /// double-click to maximize, caption buttons) and invisible edge zones resize the window.
     pub custom_titlebar: bool,
+    /// The window has the desktop's own title bar: the OS or the window manager draws its frame,
+    /// icon and title. Set by the desktop app when it opens the window; `false` for embedders
+    /// without a window of their own.
+    pub desktop_frame: bool,
     /// Last window title sent to the OS (`ViewportCommand::Title`, see `chrome::sync_window_title`):
     /// sent again only when it changes, so idle frames don't spam the backend.
     pub(crate) last_window_title: String,
diff --git a/docs/control-protocol.md b/docs/control-protocol.md
index 9357927f0..5f70424ce 100644
--- a/docs/control-protocol.md
+++ b/docs/control-protocol.md
@@ -328,7 +328,8 @@ not commands, so drive them with `ui.click` if needed. Close runs `app.quit` (th
 modified documents), and empty bar space and the 5 pt window edges move and resize the window. Preferences › User
 Interface › System Title Bar (`systemTitleBar`, read when the app starts) gives the window its OS decorations back
 instead: the OS title then shows the active document (`*name — VectorCraft` with unsaved changes) and the app bar
-drops its brand mark. On macOS the window buttons are centred on the app bar; the web build is unchanged.
+drops its brand mark. On Linux the app bar also drops its brand mark whenever the desktop draws the window's frame, with
+System Title Bar on or off. On macOS the window buttons are centred on the app bar; the web build is unchanged.
 
 Fill/Stroke chips and panel shortcuts: the Control bar's and Properties' Fill and Stroke chips bring their proxy
 forward (`paint.toggleActive {fill}`) and open a popover with the Swatches panel (Shift-click: the Color panel's mixer);