diff --git a/demos/interactive_demo.mjs b/demos/interactive_demo.mjs
index f8d9f2a..f62857d 100644
--- a/demos/interactive_demo.mjs
+++ b/demos/interactive_demo.mjs
@@ -47,9 +47,23 @@ let renderUniformBuffer = null;
 let dpr = 1;
 
 function resizeCanvas() {
-  dpr = Math.min(window.devicePixelRatio || 1, 2);
-  canvas.width = Math.round(window.innerWidth * dpr);
-  canvas.height = Math.round(window.innerHeight * dpr);
+  /* Neither dimension of the backing store may exceed the device's
+     maxTextureDimension2D (8192 by default, and this demo does not raise
+     it). Past that the swap-chain texture is invalid and nothing renders
+     at all - a black canvas with the controls still drawn on top. Since
+     the DPR scaling below multiplies the CSS size, a window wider than
+     maxTextureDimension2D / 2 would otherwise cross the limit on any
+     Retina display. */
+  const maxDim = device?.limits?.maxTextureDimension2D ?? 8192;
+  const cssWidth = Math.max(1, window.innerWidth);
+  const cssHeight = Math.max(1, window.innerHeight);
+  const fit = Math.min(maxDim / cssWidth, maxDim / cssHeight);
+
+  /* dpr stays the true CSS-to-backing-store scale after clamping, because
+     pointer coordinates and the influence radius are converted with it. */
+  dpr = Math.min(window.devicePixelRatio || 1, 2, fit);
+  canvas.width = Math.round(cssWidth * dpr);
+  canvas.height = Math.round(cssHeight * dpr);
   if (device && renderUniformBuffer) {
     device.queue.writeBuffer(renderUniformBuffer, 0, new Float32Array([canvas.width, canvas.height, 0, 0]));
   }
diff --git a/misc/run_headless_tests.js b/misc/run_headless_tests.js
index 725cfdb..2268f34 100644
--- a/misc/run_headless_tests.js
+++ b/misc/run_headless_tests.js
@@ -150,6 +150,43 @@ async function runDemoSmokeTest(browser) {
     failures.push(`canvas has no backing store (${canvas.w}x${canvas.h})`);
   }
 
+  /*
+   * Regression guard: the canvas backing store must never exceed the
+   * device's maxTextureDimension2D. Past that the swap-chain texture is
+   * invalid and the demo renders nothing - a black canvas with the
+   * controls still drawn on top, and no thrown error to notice.
+   *
+   * This is easy to reintroduce because resizeCanvas() multiplies the CSS
+   * size by devicePixelRatio, so on a Retina display any window wider
+   * than half the limit crosses it. A wide viewport is used here because
+   * the default test window is nowhere near large enough to catch it.
+   */
+  const wide = await browser.newPage();
+  try {
+    await wide.setViewport({ width: 5000, height: 1000, deviceScaleFactor: 2 });
+    await wide.goto('http://127.0.0.1:8000/demos/interactive_demo.html', {
+      waitUntil: 'domcontentloaded',
+      timeout: 30000
+    });
+    await new Promise(r => setTimeout(r, 5000));
+    const big = await wide.evaluate(async () => {
+      const c = document.getElementById('canvas');
+      const adapter = await navigator.gpu.requestAdapter();
+      const device = await adapter.requestDevice();
+      return { w: c.width, h: c.height, max: device.limits.maxTextureDimension2D };
+    });
+    if (big.w > big.max || big.h > big.max) {
+      failures.push(
+        `canvas ${big.w}x${big.h} exceeds maxTextureDimension2D ${big.max} ` +
+        `at a 5000x1000 viewport; the demo will render black`
+      );
+    } else {
+      console.log(`  wide viewport: canvas ${big.w}x${big.h} within limit ${big.max}`);
+    }
+  } finally {
+    await wide.close();
+  }
+
   // Every control the demo wires up must exist, or an addEventListener
   // call threw and the rest of the module never ran.
   const missing = await page.evaluate(() => {