diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 613f18f98..f851adb58 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -122,6 +122,8 @@ mod panel_reorder_tests;
 #[cfg(test)]
 mod panel_width_tests;
 #[cfg(test)]
+mod pen_mode_tests;
+#[cfg(test)]
 mod perf_tests;
 #[cfg(test)]
 mod plugin_panel_tests;
@@ -280,6 +282,8 @@ pub struct UiState {
     pub left_width: f32,
     pub right_width: f32,
     pub right_tab: RightTab,
+    /// The tab of the previous frame, to see the right panel change mode.
+    pub last_right_tab: RightTab,
     pub left_tab: LeftTab,
     pub pages_open: bool,
     pub expanded: BTreeSet<NodeId>,
@@ -400,6 +404,7 @@ impl Default for UiState {
             left_width: PANEL_DEFAULT,
             right_width: PANEL_DEFAULT,
             right_tab: RightTab::Design,
+            last_right_tab: RightTab::Design,
             left_tab: LeftTab::File,
             pages_open: true,
             expanded: BTreeSet::new(),
@@ -610,6 +615,19 @@ impl FigApp {
         }
     }
 
+    /// Leaving Design ends a pen path as Escape does and goes back to Move: Prototype and Inspect
+    /// don't draw (#307). Checked as the frame starts (the control channel) and after the panels
+    /// and shortcuts (the mode switcher, the tabs, Shift+E/Shift+D), before the canvas sees more.
+    fn end_pen_outside_design(&mut self) {
+        if self.ui.right_tab == self.ui.last_right_tab {
+            return;
+        }
+        self.ui.last_right_tab = self.ui.right_tab;
+        if self.ui.right_tab != RightTab::Design && self.session.tool.tool == figcraft_engine::tools::ToolId::Pen {
+            self.run("tool.set", json!({"tool": "move"}));
+        }
+    }
+
     /// Once a frame, after the panels: a preview nothing asked for this frame ends.
     fn end_unwanted_text_preview(&mut self, ctx: &egui::Context) {
         if !std::mem::take(&mut self.ui.text_preview_wanted) {
@@ -984,6 +1002,7 @@ impl FigApp {
         widgets::set_nudge(&ctx, self.session.prefs.nudge_small, self.session.prefs.nudge_big);
         // The Inspect tab measures on hover without Alt.
         self.session.tool.redlines = self.ui.right_tab == RightTab::Inspect;
+        self.end_pen_outside_design();
         if self.ui.present.is_some() {
             present::show(self, ui);
             // What went wrong while presenting (a widget's plugin failing) shows over it.
@@ -1086,6 +1105,7 @@ impl FigApp {
         variable_ui::picker(self, &ctx);
         style_picker::show(self, &ctx);
         self.end_unwanted_text_preview(&ctx);
+        self.end_pen_outside_design();
         dialogs::show(self, &ctx);
         self.toast_ui(&ctx);
         // A rename started after the layers panel drew (Cmd/Ctrl+R, a double-click) opens its field
diff --git a/crates/ui-egui/src/pen_mode_tests.rs b/crates/ui-egui/src/pen_mode_tests.rs
new file mode 100644
index 000000000..6fa54959d
--- /dev/null
+++ b/crates/ui-egui/src/pen_mode_tests.rs
@@ -0,0 +1,94 @@
+//! Leaving Design with a pen path open (#307): the path ends as Escape ends it, the tool goes back
+//! to Move, and the canvas of Prototype or Inspect takes no more pen points. Driven by the panel
+//! keys and by the toolbar's mode switcher.
+
+use egui::accesskit::Role;
+use egui::{Event, Key, Modifiers, Pos2, pos2};
+use figcraft_engine::Session;
+use figcraft_engine::tools::ToolId;
+use serde_json::json;
+
+use crate::RightTab;
+use crate::layers_drag_tests::Ui;
+
+fn press(u: &mut Ui, key: Key, modifiers: Modifiers) {
+    u.frame(vec![
+        Event::Key { key, physical_key: None, pressed: true, repeat: false, modifiers },
+        Event::Key { key, physical_key: None, pressed: false, repeat: false, modifiers },
+    ]);
+}
+
+fn click(u: &mut Ui, p: Pos2) {
+    u.button(p, true);
+    u.button(p, false);
+    u.frame(vec![]);
+}
+
+fn layers(u: &Ui) -> usize {
+    let doc = u.app.session.doc().unwrap();
+    doc.node(u.app.session.page().unwrap()).unwrap().children.len()
+}
+
+/// The middle of the toolbar's mode button named `label`, found in the AccessKit tree.
+fn mode_button(u: &mut Ui, label: &str) -> Pos2 {
+    u.ctx.enable_accesskit();
+    u.frame(vec![]);
+    let out = u.frame_output(vec![]);
+    let nodes = out.platform_output.accesskit_update.expect("an AccessKit update").nodes;
+    let n = nodes.iter().map(|(_, n)| n).find(|n| n.role() == Role::Button && n.label() == Some(label)).expect(label);
+    let b = n.bounds().expect("bounds");
+    pos2(((b.x0 + b.x1) / 2.0) as f32, ((b.y0 + b.y1) / 2.0) as f32)
+}
+
+/// A pen path with two anchors still open on an empty page.
+fn drawing() -> Ui {
+    let mut u = Ui::new(Session::new());
+    u.app.run("tool.set", json!({"tool": "pen"}));
+    click(&mut u, pos2(600.0, 400.0));
+    click(&mut u, pos2(700.0, 450.0));
+    assert_eq!(u.app.session.tool.pen.as_ref().map(|p| p.points.len()), Some(2), "the path is open");
+    u
+}
+
+#[test]
+fn switching_mode_ends_the_pen_path_as_escape_does() {
+    let mut esc = drawing();
+    press(&mut esc, Key::Escape, Modifiers::NONE);
+    assert!(esc.app.session.tool.pen.is_none());
+    let finished = layers(&esc);
+    assert_eq!(finished, 1, "Escape keeps the two-anchor path");
+
+    // Shift+E is Prototype, Shift+D is Inspect.
+    for key in [Key::E, Key::D] {
+        let mut u = drawing();
+        press(&mut u, key, Modifiers::SHIFT);
+        assert_ne!(u.app.ui.right_tab, RightTab::Design, "{key:?}");
+        assert!(u.app.session.tool.pen.is_none(), "{key:?}: the path is finished");
+        assert_eq!(u.app.session.tool.tool, ToolId::Move, "{key:?}: back to Move");
+        assert_eq!(layers(&u), finished, "{key:?}: the path is kept as Escape keeps it");
+        // The canvas takes no more pen points.
+        click(&mut u, pos2(800.0, 300.0));
+        assert!(u.app.session.tool.pen.is_none(), "{key:?}: a click starts no path");
+        assert_eq!(layers(&u), finished, "{key:?}: a click adds nothing");
+    }
+}
+
+#[test]
+fn the_mode_switcher_ends_the_pen_path_too() {
+    let finished = {
+        let mut esc = drawing();
+        press(&mut esc, Key::Escape, Modifiers::NONE);
+        layers(&esc)
+    };
+    // Design is already the mode while the pen draws: pressing it still leaves the pen, as it leaves
+    // the pencil of Draw.
+    for (label, tab) in [("Prototype", RightTab::Prototype), ("Inspect", RightTab::Inspect), ("Design", RightTab::Design)] {
+        let mut u = drawing();
+        let at = mode_button(&mut u, label);
+        click(&mut u, at);
+        assert_eq!(u.app.ui.right_tab, tab, "{label}");
+        assert!(u.app.session.tool.pen.is_none(), "{label}: the path is finished");
+        assert_eq!(u.app.session.tool.tool, ToolId::Move, "{label}: back to Move");
+        assert_eq!(layers(&u), finished, "{label}: the path is kept as Escape keeps it");
+    }
+}
diff --git a/crates/ui-egui/src/toolbar.rs b/crates/ui-egui/src/toolbar.rs
index 1e6e38aa1..24af4a640 100644
--- a/crates/ui-egui/src/toolbar.rs
+++ b/crates/ui-egui/src/toolbar.rs
@@ -174,7 +174,7 @@ pub fn show(app: &mut FigApp, ui: &mut Ui) {
                 }
                 1 => {
                     app.ui.right_tab = crate::RightTab::Design;
-                    if app.session.tool.tool == ToolId::Pencil {
+                    if matches!(app.session.tool.tool, ToolId::Pencil | ToolId::Pen) {
                         app.run("tool.set", json!({"tool": "move"}));
                     }
                 }