diff --git a/crates/ui-egui/src/panes.rs b/crates/ui-egui/src/panes.rs
index 69dbbe99f..9675d2a95 100644
--- a/crates/ui-egui/src/panes.rs
+++ b/crates/ui-egui/src/panes.rs
@@ -308,13 +308,29 @@ fn format_chart(app: &mut SheetApp, ui: &mut Ui) {
     ui.collapsing("Size", |ui| {
         // Keep the value being typed or dragged between frames; reloading it from the chart every frame threw the edit away.
         let draft = egui::Id::unique(("gridcraft.chart_size_draft", id));
-        let (mut w, mut h) = ui.data_mut(|d| d.get_temp::<(f32, f32)>(draft)).unwrap_or((chart.anchor.width, chart.anchor.height));
-        let a = ui.add(egui::DragValue::new(&mut w).prefix("Width ").range(40.0..=4000.0));
-        let b = ui.add(egui::DragValue::new(&mut h).prefix("Height ").range(40.0..=4000.0));
+        let current = (chart.anchor.width, chart.anchor.height);
+        let (mut w, mut h) = ui.data_mut(|d| d.get_temp::<(f32, f32)>(draft)).unwrap_or(current);
+        // A file can make a chart larger than the 4,000 points a field otherwise reaches. The
+        // range keeps such a size, so the field shows it instead of clamping it to 4,000.
+        let range = |v: f32| 40.0..=v.max(4000.0);
+        let a = ui.add(egui::DragValue::new(&mut w).prefix("Width ").range(range(current.0)));
+        let b = ui.add(egui::DragValue::new(&mut h).prefix("Height ").range(range(current.1)));
         if a.drag_stopped() || a.lost_focus() || b.drag_stopped() || b.lost_focus() {
             ui.data_mut(|d| d.remove::<(f32, f32)>(draft));
             if !ui.input(|i| i.key_pressed(egui::Key::Escape)) {
-                app.run_or_alert("chart.set", json!({"chart": id, "width": w, "height": h}));
+                // Only an edited dimension is sent: the other keeps what the chart has, however
+                // large a file made it.
+                let mut params = serde_json::Map::new();
+                params.insert("chart".into(), json!(id));
+                if w != current.0 {
+                    params.insert("width".into(), json!(w));
+                }
+                if h != current.1 {
+                    params.insert("height".into(), json!(h));
+                }
+                if params.len() > 1 {
+                    app.run_or_alert("chart.set", Json::Object(params));
+                }
             }
         } else if a.dragged() || a.has_focus() || b.dragged() || b.has_focus() {
             ui.data_mut(|d| d.insert_temp(draft, (w, h)));
diff --git a/crates/ui-egui/tests/it/chart_resize.rs b/crates/ui-egui/tests/it/chart_resize.rs
index 2ae8707df..36934fbcb 100644
--- a/crates/ui-egui/tests/it/chart_resize.rs
+++ b/crates/ui-egui/tests/it/chart_resize.rs
@@ -118,6 +118,51 @@ fn dragging_the_size_field_resizes_the_chart() {
     assert!(w1 > w0 + 20.0, "width went from {w0} to {w1}");
 }
 
+/// Makes the chart 12,000 wide and reopens the workbook from its XLSX bytes, the way a file can
+/// carry a chart larger than the 4,000 points the Size fields otherwise reach; returns its id.
+fn imported_oversized_chart(h: &mut Harness, id: u32) -> u32 {
+    {
+        let wb = std::sync::Arc::make_mut(&mut h.state_mut().session.doc_mut().unwrap().wb);
+        wb.sheet_mut(0).unwrap().charts.iter_mut().find(|c| c.id == id).unwrap().anchor.width = 12_000.0;
+    }
+    let saved = h.state_mut().run("file.saveBytes", json!({"format": "xlsx"})).unwrap();
+    h.state_mut().run("file.open", json!({"name": "wide.xlsx", "base64": saved["base64"]})).unwrap();
+    h.run_steps(4);
+    let id = h.state().session.doc().unwrap().wb.active().unwrap().charts[0].id;
+    let (w, hh) = size(h, id);
+    assert_eq!((w.round(), hh.round()), (12_000.0, 200.0), "the reader keeps the file's size");
+    id
+}
+
+/// A chart a file made 12,000 wide shows that width in the Size fields, and a new height sends
+/// the height alone, so nothing shrinks the width to the fields' 4,000 reach on the way.
+#[test]
+fn the_size_fields_keep_an_oversized_imported_chart_width_when_the_height_changes() {
+    let (mut h, id) = fixture();
+    let id = imported_oversized_chart(&mut h, id);
+    open_size_fields(&mut h, id);
+    let (width_value, height_field) = {
+        let mut fields = h.get_all_by_role(Role::SpinButton);
+        let width = fields.next().unwrap();
+        let height = fields.next().unwrap();
+        (width.value(), height.rect())
+    };
+    assert!(width_value.as_deref().is_some_and(|v| v.contains("12000")), "the field shows the file's width: {width_value:?}");
+    h.input_mut().events.push(Event::PointerMoved(height_field.center()));
+    button(&mut h, height_field.center(), true);
+    button(&mut h, height_field.center(), false);
+    for digit in ["2", "0", "1"] {
+        h.input_mut().events.push(Event::Text(digit.into()));
+        h.run_steps(2);
+    }
+    h.key_press(Key::Enter);
+    h.run_steps(2);
+    let (w, hh) = size(&h, id);
+    assert_eq!((w.round(), hh), (12_000.0, 201.0), "the width stays and the height is the typed one");
+    let (_, p) = h.state().session.journal.iter().rev().find(|(cmd, _)| cmd == "chart.set").unwrap();
+    assert!(p.get("width").is_none(), "a height edit sends no width: {p}");
+}
+
 fn right_click(h: &mut Harness, pos: egui::Pos2, wobble: egui::Vec2) {
     h.input_mut().events.push(Event::PointerMoved(pos));
     h.run_steps(2);