diff --git a/crates/ui-egui/src/dialogs.rs b/crates/ui-egui/src/dialogs.rs
index 18d112c8..abe8c87e 100644
--- a/crates/ui-egui/src/dialogs.rs
+++ b/crates/ui-egui/src/dialogs.rs
@@ -108,6 +108,9 @@ pub fn show(app: &mut SlideApp, ctx: &egui::Context) {
     let escape = ctx.input(|i| i.key_pressed(egui::Key::Escape));
     if open && !close && !escape {
         app.dialog = Some(d);
+    } else if !close && d.id == "preferences" {
+        // Esc or the window's close button: the same as Cancel.
+        restore_preferences(app, &d);
     } else if app.dialog.is_none()
         && let Some(ret) = d.params.get("returnParams").filter(|v| v.is_object()).cloned()
     {
@@ -137,6 +140,31 @@ fn buttons(ui: &mut Ui, ok_label: &str) -> (bool, bool) {
     (ok, cancel)
 }
 
+/// What the Preferences dialog can change, as it was when the dialog opened.
+fn preferences_snapshot(app: &SlideApp) -> Value {
+    json!({
+        "dark": app.ui.brightness == theme::Brightness::Dark,
+        "uiScale": app.ui.ui_scale,
+        "prefs": serde_json::to_value(&app.session.prefs).unwrap_or(Value::Null),
+    })
+}
+
+/// Puts back the settings the Preferences dialog opened with (Cancel, Esc, the close button).
+fn restore_preferences(app: &mut SlideApp, d: &Dialog) {
+    let Some(before) = d.params.get("before") else { return };
+    if let Some(dark) = before.get("dark").and_then(Value::as_bool)
+        && dark != (app.ui.brightness == theme::Brightness::Dark)
+    {
+        let _ = app.run("view.dark", json!({ "on": dark }));
+    }
+    if let Some(scale) = before.get("uiScale").and_then(Value::as_f64) {
+        app.ui.ui_scale = scale as f32;
+    }
+    if let Some(prefs) = before.get("prefs").and_then(|p| serde_json::from_value(p.clone()).ok()) {
+        app.session.prefs = prefs;
+    }
+}
+
 fn field(ui: &mut Ui, d: &mut Dialog, label: &str, key: &str, default: &str) {
     let mut v = d.get(key, default);
     ui.horizontal(|ui| {
@@ -2104,6 +2132,11 @@ fn body(app: &mut SlideApp, ui: &mut Ui, d: &mut Dialog) -> bool {
         }
         "gridOptions" => grid_options(app, ui, d),
         "preferences" => {
+            // The controls apply as they change, so the dialog remembers what it opened with and
+            // Cancel (or Esc, or the close button: see `show`) puts that back.
+            if d.params.get("before").is_none() {
+                d.params = json!({ "before": preferences_snapshot(app) });
+            }
             ui.label(egui::RichText::new("General").font(theme::bold(13.0)));
             let mut dark = app.ui.brightness == theme::Brightness::Dark;
             if ui.checkbox(&mut dark, "Dark appearance").changed() {
@@ -2130,8 +2163,11 @@ fn body(app: &mut SlideApp, ui: &mut Ui, d: &mut Dialog) -> bool {
                 ui.label("Your name (comments):");
                 ui.text_edit_singleline(&mut app.session.prefs.author);
             });
-            let (ok, _) = buttons(ui, "Done");
-            ok
+            let (ok, cancel) = buttons(ui, "Done");
+            if cancel {
+                restore_preferences(app, d);
+            }
+            ok || cancel
         }
         "photoAlbum" => photo_album_dialog(app, ui, d),
         "themeColors" => theme_colors_dialog(app, ui, d),
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index f020f5f5..9d4a681b 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -2573,6 +2573,71 @@ mod tests {
         assert!((harness.state().session.prefs.grid_spacing - 6.0).abs() < 1e-9);
     }
 
+    /// Preferences (#752): Cancel, Esc and the window's close button put back what the dialog
+    /// changed while it was open; Done keeps it.
+    #[test]
+    fn preferences_cancel_restores_the_settings_done_keeps_them() {
+        use egui_kittest::kittest::Queryable;
+        let mut harness = egui_kittest::Harness::builder().with_size(egui::vec2(1200.0, 800.0)).build_ui_state(
+            |ui, app: &mut SlideApp| {
+                app.logic(ui.ctx());
+                app.ui(ui);
+            },
+            SlideApp::new(Session::with_new(), Services::default()),
+        );
+        harness.run_steps(2);
+        let before = harness.state().session.prefs.clone();
+        let dark_before = harness.state().ui.brightness;
+        let change = |harness: &mut egui_kittest::Harness<'static, SlideApp>| {
+            harness.state_mut().run("app.preferences", json!({})).unwrap();
+            harness.run_steps(2);
+            for label in ["Dark appearance", "Show smart guides", "Snap objects to grid"] {
+                harness
+                    .query_all_by_role_and_label(egui::accesskit::Role::CheckBox, label)
+                    .next()
+                    .unwrap_or_else(|| panic!("no {label} checkbox"))
+                    .click_accesskit();
+                harness.run_steps(2);
+            }
+            assert_ne!(harness.state().ui.brightness, dark_before, "the dialog previews the appearance");
+            assert_ne!(harness.state().session.prefs.smart_guides, before.smart_guides);
+        };
+        let unchanged = |harness: &egui_kittest::Harness<'static, SlideApp>, how: &str| {
+            let s = harness.state();
+            assert!(s.dialog.is_none(), "{how} closes Preferences");
+            assert_eq!(s.ui.brightness, dark_before, "{how} restores the appearance");
+            assert_eq!(s.session.prefs.smart_guides, before.smart_guides, "{how} restores smart guides");
+            assert_eq!(s.session.prefs.snap_to_grid, before.snap_to_grid, "{how} restores snap to grid");
+        };
+
+        change(&mut harness);
+        harness
+            .query_all_by_role_and_label(egui::accesskit::Role::Button, "Cancel")
+            .next()
+            .unwrap_or_else(|| panic!("no Cancel button"))
+            .click_accesskit();
+        harness.run_steps(2);
+        unchanged(&harness, "Cancel");
+
+        change(&mut harness);
+        harness.key_press(egui::Key::Escape);
+        harness.run_steps(2);
+        unchanged(&harness, "Esc");
+
+        change(&mut harness);
+        harness
+            .query_all_by_role_and_label(egui::accesskit::Role::Button, "Done")
+            .next()
+            .unwrap_or_else(|| panic!("no Done button"))
+            .click_accesskit();
+        harness.run_steps(2);
+        let s = harness.state();
+        assert!(s.dialog.is_none(), "Done closes Preferences");
+        assert_ne!(s.ui.brightness, dark_before, "Done keeps the appearance");
+        assert_ne!(s.session.prefs.smart_guides, before.smart_guides, "Done keeps smart guides");
+        assert_ne!(s.session.prefs.snap_to_grid, before.snap_to_grid, "Done keeps snap to grid");
+    }
+
     fn canvas_harness() -> egui_kittest::Harness<'static, SlideApp> {
         let mut harness = egui_kittest::Harness::builder().with_size(egui::vec2(1200.0, 800.0)).build_ui_state(
             |ui, app: &mut SlideApp| {