diff --git a/test/integration/image-optimizer/app/pages/api/no-header.js b/test/integration/image-optimizer/app/pages/api/no-header.js
new file mode 100644
index 0000000000000..287931027217f
--- /dev/null
+++ b/test/integration/image-optimizer/app/pages/api/no-header.js
@@ -0,0 +1,5 @@
+export default function handler(_req, res) {
+  // Intentionally missing Content-Type header so that
+  // the fallback is not served when optimization fails
+  res.end('foo')
+}
diff --git a/test/integration/image-optimizer/test/util.ts b/test/integration/image-optimizer/test/util.ts
index f1fd063f837c0..b5f517b69e38c 100644
--- a/test/integration/image-optimizer/test/util.ts
+++ b/test/integration/image-optimizer/test/util.ts
@@ -887,7 +887,7 @@ export function runTests(ctx) {
   })
 
   it('should fail when internal url is not an image', async () => {
-    const url = `//<h1>not-an-image</h1>`
+    const url = `/api/no-header`
     const query = { url, w: ctx.w, q: 39 }
     const opts = { headers: { accept: 'image/webp' } }
     const res = await fetchViaHTTP(ctx.appPort, '/_next/image', query, opts)