diff --git a/lib/react/SimpleGraphicsSVG.tsx b/lib/react/SimpleGraphicsSVG.tsx
index 3a73f9f..4e3f3c8 100644
--- a/lib/react/SimpleGraphicsSVG.tsx
+++ b/lib/react/SimpleGraphicsSVG.tsx
@@ -30,16 +30,16 @@ export function SimpleGraphicsSVG({ graphics }: { graphics: GraphicsObject }) {
     for (const p of pts) consider(p.x, p.y)
   }
   for (const r of rects) {
-    const x = (r as any).x ?? 0
-    const y = (r as any).y ?? 0
+    const x = r.center.x - r.width / 2
+    const y = r.center.y - r.height / 2
     const w = (r as any).width ?? 0
     const h = (r as any).height ?? 0
     consider(x, y)
     consider(x + w, y + h)
   }
   for (const c of circles) {
-    const x = (c as any).x ?? 0
-    const y = (c as any).y ?? 0
+    const x = c.center.x
+    const y = c.center.y
     const rad = (c as any).radius ?? 1
     consider(x - rad, y - rad)
     consider(x + rad, y + rad)
@@ -74,12 +74,12 @@ export function SimpleGraphicsSVG({ graphics }: { graphics: GraphicsObject }) {
       {rects.map((r: any, i: number) => (
         <rect
           key={`rect-${i}`}
-          x={r.x ?? 0}
-          y={r.y ?? 0}
+          x={r.center.x - r.width / 2}
+          y={r.center.y - r.height / 2}
           width={r.width ?? 0}
           height={r.height ?? 0}
-          fill="none"
-          stroke={r.strokeColor ?? "black"}
+          fill={r.fill ?? "none"}
+          stroke={r.stroke ?? "black"}
           strokeWidth={r.strokeWidth ?? 1}
         />
       ))}
@@ -97,11 +97,11 @@ export function SimpleGraphicsSVG({ graphics }: { graphics: GraphicsObject }) {
       {circles.map((c: any, i: number) => (
         <circle
           key={`circle-${i}`}
-          cx={c.x ?? 0}
-          cy={c.y ?? 0}
+          cx={c.center.x}
+          cy={c.center.y}
           r={c.radius ?? 1.5}
-          fill={c.fillColor ?? "none"}
-          stroke={c.strokeColor ?? "black"}
+          fill={c.fill ?? "none"}
+          stroke={c.stroke ?? "black"}
           strokeWidth={c.strokeWidth ?? 1}
         />
       ))}
diff --git a/tests/fallback-shapes.test.tsx b/tests/fallback-shapes.test.tsx
new file mode 100644
index 0000000..04ed2f5
--- /dev/null
+++ b/tests/fallback-shapes.test.tsx
@@ -0,0 +1,69 @@
+import { expect, test } from "bun:test"
+import type { GraphicsObject } from "graphics-debug"
+import type { ReactElement } from "react"
+import { SimpleGraphicsSVG } from "../lib/react/SimpleGraphicsSVG"
+
+const {
+  renderToStaticMarkup,
+}: {
+  renderToStaticMarkup: (element: ReactElement) => string
+} = require("react-dom/server")
+
+const render = (graphics: GraphicsObject) =>
+  renderToStaticMarkup(<SimpleGraphicsSVG graphics={graphics} />)
+
+test("fallback rectangles use their center and include their actual bounds", () => {
+  const svg = render({
+    rects: [{ center: { x: 100, y: -50 }, width: 20, height: 10 }],
+  })
+
+  expect(svg).toContain('x="90" y="-55" width="20" height="10"')
+  expect(svg).toContain('viewBox="80 -65 40 30"')
+})
+
+test("fallback circles use their center and include their actual bounds", () => {
+  const svg = render({
+    circles: [{ center: { x: -40, y: 70 }, radius: 5 }],
+  })
+
+  expect(svg).toContain('cx="-40" cy="70" r="5"')
+  expect(svg).toContain('viewBox="-55 55 30 30"')
+})
+
+test("the viewBox includes separated rectangles and circles", () => {
+  const svg = render({
+    rects: [{ center: { x: 100, y: -50 }, width: 20, height: 10 }],
+    circles: [{ center: { x: -40, y: 70 }, radius: 5 }],
+  })
+
+  expect(svg).toContain('viewBox="-55 -65 175 150"')
+})
+
+test("fallback shapes use the fill and stroke fields from GraphicsObject", () => {
+  const svg = render({
+    rects: [
+      {
+        center: { x: 0, y: 0 },
+        width: 20,
+        height: 10,
+        fill: "red",
+        stroke: "blue",
+      },
+    ],
+    circles: [
+      { center: { x: 40, y: 0 }, radius: 5, fill: "green", stroke: "purple" },
+    ],
+  })
+
+  expect(svg).toContain('fill="red" stroke="blue"')
+  expect(svg).toContain('fill="green" stroke="purple"')
+})
+
+test("rectangles centered at the origin extend to both sides of it", () => {
+  const svg = render({
+    rects: [{ center: { x: 0, y: 0 }, width: 20, height: 10 }],
+  })
+
+  expect(svg).toContain('x="-10" y="-5"')
+  expect(svg).toContain('viewBox="-20 -15 40 30"')
+})