diff --git a/crates/ui-egui/src/chrome.rs b/crates/ui-egui/src/chrome.rs
index f828ae91..ff8fa29b 100644
--- a/crates/ui-egui/src/chrome.rs
+++ b/crates/ui-egui/src/chrome.rs
@@ -843,6 +843,20 @@ mod tests {
         assert_eq!(after, before);
     }
 
+    /// At 115% the app bar fits a wide window exactly: it must not scroll sideways by a rounding error.
+    #[test]
+    fn the_app_bar_does_not_scroll_at_115_percent() {
+        let w = 1400.0;
+        let mut h = test_window::open_scaled(app(), vec2(w, 900.0), 1.15);
+        assert_eq!(h.ctx.pixels_per_point(), 1.15);
+        let before = [rect(&h, "Help"), rect(&h, "Share")];
+        assert!(before.iter().all(|r| r.max.x <= w), "{before:?}");
+        wheel(&mut h, before[0].center(), vec2(0.0, -3000.0));
+        wheel(&mut h, before[0].center(), vec2(-3000.0, 0.0));
+        let after = [rect(&h, "Help"), rect(&h, "Share")];
+        assert_eq!(after, before, "the app bar scrolled sideways although everything fits");
+    }
+
     #[test]
     fn a_scrolled_bar_keeps_its_captions_on_one_line() {
         let mut app = app();
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index c003154a..fcd9ddff 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -1330,11 +1330,16 @@ pub(crate) mod test_window {
     }
 
     /// The window at `size` with a new document open.
-    pub fn open(mut app: crate::DesignApp, size: egui::Vec2) -> Harness<'static, Window> {
+    pub fn open(app: crate::DesignApp, size: egui::Vec2) -> Harness<'static, Window> {
+        open_scaled(app, size, 1.0)
+    }
+
+    /// The window at a size in points and a scale, with a new document open.
+    pub fn open_scaled(mut app: crate::DesignApp, size: egui::Vec2, pixels_per_point: f32) -> Harness<'static, Window> {
         if app.session.active().is_none() {
             app.run("file.new", serde_json::json!({})).unwrap();
         }
-        let mut h = Harness::builder().with_size(size).with_max_steps(1000).build_ui_state(
+        let mut h = Harness::builder().with_size(size).with_pixels_per_point(pixels_per_point).with_max_steps(1000).build_ui_state(
             |ui, w: &mut Window| {
                 // The builder runs a frame before the texture size can be raised: skip it.
                 if !w.ready {