diff --git a/crates/ui/src/layout.rs b/crates/ui/src/layout.rs
index 7e4e7f4c9dabd518821f5fabe695ed762cb7703a..5a9f4203eb805b4390196afefe8b77f0e118e065 100644
--- a/crates/ui/src/layout.rs
+++ b/crates/ui/src/layout.rs
@@ -62,7 +62,7 @@ fn resolve(nodes: &mut [Built], popup: &[usize], index: usize, states: &HashMap<
     let around = match anchor {
         Anchor::Point([x, y]) => [x, y, x, y],
         Anchor::Dialog | Anchor::Top => [0.0; 4],
-        Anchor::Below(id) | Anchor::Right(id) | Anchor::Over(id) => {
+        Anchor::Below(id) | Anchor::Tip(id) | Anchor::Right(id) | Anchor::Over(id) => {
             let (rect, holder) = laid_out(id).unwrap_or_default();
             let [left, top, right, bottom] = rect;
             match anchor {
diff --git a/crates/ui/src/lib.rs b/crates/ui/src/lib.rs
index 48c67718855d2ad80f955ac8b65144cad820950f..796580640613a36bbf3d6d83d5d47cc77bad1220 100644
--- a/crates/ui/src/lib.rs
+++ b/crates/ui/src/lib.rs
@@ -230,6 +230,8 @@ pub enum Anchor {
     /// Over the box from its corner, the popup's contents covering it, as a combo box opens
     /// into its own list; at least as wide as it.
     Over(Id),
+    /// Under the box, centred on it, as a tooltip shows.
+    Tip(Id),
     /// At a point, as a context menu opens.
     Point([f32; 2]),
     /// Centred across the window near its top, over the interface, which dims, as a dialog
@@ -252,6 +254,10 @@ impl Anchor {
             Anchor::Below(_) | Anchor::Point(_) => Some(1),
             Anchor::Right(_) => Some(0),
             Anchor::Over(_) => None,
+            Anchor::Tip(_) if axis == 0 => {
+                return ((around[0] + around[2] - size) / 2.0).clamp(POPUP_MARGIN, most);
+            }
+            Anchor::Tip(_) => Some(1),
             Anchor::Dialog | Anchor::Top if axis == 0 => {
                 return ((room - size) / 2.0).max(POPUP_MARGIN);
             }
@@ -593,6 +599,7 @@ impl Placed {
         } = self;
         let pivot = match anchor {
             Anchor::Below(_) | Anchor::Point(_) => [around[0], around[3]],
+            Anchor::Tip(_) => [(around[0] + around[2]) / 2.0, around[3]],
             Anchor::Right(_) => [around[2], around[1]],
             Anchor::Over(_) => [around[0], around[1]],
             Anchor::Dialog | Anchor::Top => [(rect[0] + rect[2]) / 2.0, rect[1]],
diff --git a/crates/ui/src/popup.rs b/crates/ui/src/popup.rs
index 06594aff22411a47a77440930f692b2016e47dcd..f11931f28ee16f2386b9a71a7539fe3bf2da3203 100644
--- a/crates/ui/src/popup.rs
+++ b/crates/ui/src/popup.rs
@@ -220,7 +220,7 @@ pub fn submenus(ui: &mut Ui, id: Id, items: &[Item], submenu: impl Fn(usize) ->
 }
 
 /// Shows `title`, with the `keys` that run it and a `description` under it, in a tooltip
-/// below the box built last while the pointer rests on it or on a box inside it:
+/// centred below the box built last while the pointer rests on it or on a box inside it:
 /// after a delay, or at once while another has just shown. A press or the wheel hides it
 /// until the pointer leaves. It names the box to assistive technology, or where the box has
 /// no role, the unnamed controls inside it.
@@ -316,7 +316,7 @@ fn tooltip_below(
         radius: 4.0,
         pad: [8.0, 5.0],
         gap: 3.0,
-        anchor: Some(Anchor::Below(part.unwrap_or(id))),
+        anchor: Some(Anchor::Tip(part.unwrap_or(id))),
         ..Spec::default()
     };
     ui.open_as(id.child("tooltip"), spec);
diff --git a/crates/ui/src/tests.rs b/crates/ui/src/tests.rs
index 2d2a061f2f0bcedd0fbb8d8439906edc4f7cc7a2..0834cd0bdb40cf4cfe324733979497d6a72cacc7 100644
--- a/crates/ui/src/tests.rs
+++ b/crates/ui/src/tests.rs
@@ -1266,6 +1266,48 @@ fn tooltips_wait_then_switch_at_once_and_hide_on_press_until_left() {
     assert!(rest(&mut ui, 500)[0].is_some());
 }
 
+#[test]
+fn a_tooltip_centres_under_its_control_and_shifts_only_to_stay_in_the_window() {
+    let mut ui = Ui::new(Theme::dark(), DOUBLE_CLICK);
+    let mut shown_at = |x: f32| {
+        ui.event(Event::PointerMoved([x + 10.0, 110.0]));
+        let mut tip = None;
+        for _ in 0..40 {
+            frame(&mut ui, |ui| {
+                let id = ui.open(
+                    "tool",
+                    Spec {
+                        flags: Flags::CLICKABLE | Flags::FLOAT,
+                        size: [px(20.0), px(20.0)],
+                        position: [x, 100.0],
+                        ..Spec::default()
+                    },
+                );
+                ui.close();
+                popup::tooltip(ui, "Bold", "Ctrl+B", Some("Makes the selected text bold."));
+                tip = Some(id.child("tooltip"));
+            });
+        }
+        ui.laid_out(tip.unwrap()).unwrap()
+    };
+    let middle = shown_at(190.0);
+    assert_eq!(middle[1], 120.0 + popup::PAD, "under the control");
+    assert!(
+        ((middle[0] + middle[2]) / 2.0 - 200.0).abs() <= 0.5,
+        "centred on it: {middle:?}"
+    );
+    let width = middle[2] - middle[0];
+    assert_eq!(
+        shown_at(2.0)[..3],
+        [POPUP_MARGIN, 120.0 + popup::PAD, POPUP_MARGIN + width]
+    );
+    assert_eq!(
+        shown_at(378.0)[0],
+        400.0 - POPUP_MARGIN - width,
+        "shifted only to fit"
+    );
+}
+
 #[test]
 fn a_popup_opens_beside_a_box_first_laid_out_in_the_same_frame() {
     let mut ui = Ui::new(Theme::dark(), DOUBLE_CLICK);