diff --git a/demo/bundle-freshness.mjs b/demo/bundle-freshness.mjs
index 1f72a8da..f3078948 100644
--- a/demo/bundle-freshness.mjs
+++ b/demo/bundle-freshness.mjs
@@ -1,8 +1,24 @@
+import { existsSync } from 'node:fs';
+import { resolve } from 'node:path';
+import { pathToFileURL } from 'node:url';
 import { sourceFingerprint } from '../scripts/source-fingerprint.mjs';
 
+const fingerprintForTree = async (root) => {
+  const modulePath = resolve(root, 'scripts/source-fingerprint.mjs');
+  if (!existsSync(modulePath)) return sourceFingerprint(root);
+  const module = await import(pathToFileURL(modulePath).href);
+  if (typeof module.sourceFingerprint !== 'function') {
+    throw new Error(`${modulePath} does not export sourceFingerprint`);
+  }
+  return module.sourceFingerprint(root);
+};
+
 /** Refuse measurements/screenshots made by a committed bundle from old source. */
 export async function assertFreshDemoBundle(page, root = process.cwd()) {
-  const expected = sourceFingerprint(root);
+  // A comparative performance run may load an older tree whose fingerprint
+  // contract is intentionally different from the candidate's. Validate that
+  // tree with the implementation that built it, not with today's algorithm.
+  const expected = await fingerprintForTree(root);
   const loaded = await page.evaluate(() => globalThis.__HOUSEPLAN_BUILD_FINGERPRINT__ ?? null);
   if (loaded !== expected) {
     throw new Error(
diff --git a/test/bundle-freshness.test.mjs b/test/bundle-freshness.test.mjs
index 235b81c5..dc67ff68 100644
--- a/test/bundle-freshness.test.mjs
+++ b/test/bundle-freshness.test.mjs
@@ -39,3 +39,19 @@ test('bundle freshness rejects a missing or stale fingerprint', async () => {
     rmSync(root, { recursive: true, force: true });
   }
 });
+
+test('bundle freshness uses the target tree fingerprint contract', async () => {
+  const root = fixtureRoot();
+  try {
+    mkdirSync(resolve(root, 'scripts'), { recursive: true });
+    writeFileSync(
+      resolve(root, 'scripts/source-fingerprint.mjs'),
+      "export const sourceFingerprint = () => 'legacy-tree-fingerprint';\n",
+      'utf8',
+    );
+    const page = { evaluate: async () => 'legacy-tree-fingerprint' };
+    assert.equal(await assertFreshDemoBundle(page, root), 'legacy-tree-fingerprint');
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});