diff --git a/crates/engine/src/vector_cmds/tests.rs b/crates/engine/src/vector_cmds/tests.rs
index 11a4b511e0..21207d3e96 100644
--- a/crates/engine/src/vector_cmds/tests.rs
+++ b/crates/engine/src/vector_cmds/tests.rs
@@ -796,6 +796,31 @@ fn shape_info_bounds_of_curved_shapes_are_exact() {
     }
 }
 
+#[test]
+fn shape_create_negative_size_rect_covers_the_ellipse_box() {
+    // Issue #4203: a rectangle with a negative width spanned x 50..70 while the ellipse and
+    // polygon with the same `rect` spanned 30..50.
+    for depth in [8, 16, 32] {
+        let mut s = session(100, 60, depth);
+        let ell = s.execute("shape.create", json!({"kind": "ellipse", "rect": [50, 10, -20, 30], "fill": "#0000ff"})).unwrap()["bounds"].clone();
+        assert_eq!(ell, json!([30, 10, 20, 30]), "{depth}-bit");
+        for params in [
+            json!({"kind": "rect", "rect": [50, 10, -20, 30], "fill": "#0000ff"}),
+            json!({"kind": "roundedRect", "rect": [50, 10, -20, 30], "radii": 5, "fill": "#0000ff"}),
+            json!({"kind": "rect", "rect": [50, 40, -20, -30], "fill": "#0000ff"}),
+        ] {
+            let r = s.execute("shape.create", params.clone()).unwrap();
+            assert_eq!(r["bounds"], ell, "{params} at {depth}-bit");
+            let sh = shape(&s, r["layer"].as_u64().unwrap());
+            let c = sh.cache.as_ref().unwrap();
+            let fmt = c.format();
+            let alpha = |x: i32, y: i32| photocraft_raster::to_rgba(&fmt, &c.read_region(photocraft_doc::Rect::from_xywh(x, y, 1, 1)))[3];
+            assert!(alpha(40, 25) > 0.99, "{params} at {depth}-bit");
+            assert!(alpha(60, 25) < 0.01, "{params} at {depth}-bit");
+        }
+    }
+}
+
 /// Two overlapping 40×40 rectangle shape layers ("Rectangle 1" black below, "Rectangle 2" grey
 /// above, overlapping by 20×20) with both selected, like the Layers panel in #2400.
 fn two_selected_rects(depth: u32) -> (Session, u64, u64) {
diff --git a/crates/vector/src/shapes.rs b/crates/vector/src/shapes.rs
index a459ba816e..b154a47325 100644
--- a/crates/vector/src/shapes.rs
+++ b/crates/vector/src/shapes.rs
@@ -29,9 +29,11 @@ pub fn clamp_radii(w: f64, h: f64, radii: [f64; 4]) -> [f64; 4] {
     r.map(|v| v * f)
 }
 
-/// Rectangle with corner radii `[top-left, top-right, bottom-right, bottom-left]`.
+/// Rectangle with corner radii `[top-left, top-right, bottom-right, bottom-left]`. A negative
+/// width or height extends from the origin to the left or up, like [`ellipse`] and [`polygon`].
 pub fn rounded_rect(x: f64, y: f64, w: f64, h: f64, radii: [f64; 4]) -> Path {
-    let (w, h) = (w.abs(), h.abs());
+    let (x, w) = if w < 0.0 { (x + w, -w) } else { (x, w) };
+    let (y, h) = if h < 0.0 { (y + h, -h) } else { (y, h) };
     let [tl, tr, br, bl] = clamp_radii(w, h, radii);
     if tl <= 0.0 && tr <= 0.0 && br <= 0.0 && bl <= 0.0 {
         return rect(x, y, w, h);
@@ -143,6 +145,20 @@ mod tests {
         assert_eq!(clamp_radii(10.0, 10.0, [10.0; 4]), [5.0; 4]);
     }
 
+    #[test]
+    fn negative_size_rect_extends_from_its_origin_like_the_ellipse() {
+        // Issue #4203: a negative width/height drew the rectangle on the far side of its origin.
+        let want = ellipse(50.0, 10.0, -20.0, 30.0).control_bounds().unwrap();
+        let want_neg_h = ellipse(50.0, 40.0, -20.0, -30.0).control_bounds().unwrap();
+        for radii in [[0.0; 4], [5.0; 4]] {
+            let b = rounded_rect(50.0, 10.0, -20.0, 30.0, radii).control_bounds().unwrap();
+            assert_eq!(b, want, "radii {radii:?}");
+            assert_eq!(b, (30.0, 10.0, 50.0, 40.0), "radii {radii:?}");
+            let b = rounded_rect(50.0, 40.0, -20.0, -30.0, radii).control_bounds().unwrap();
+            assert_eq!(b, want_neg_h, "radii {radii:?}");
+        }
+    }
+
     #[test]
     fn star_vertices() {
         assert_eq!(polygon(0.0, 0.0, 10.0, 10.0, 5, 0.5).subpaths[0].knots.len(), 10);