diff --git a/CHANGELOG.md b/CHANGELOG.md
index dad661d9..bb3b7a4e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ Format based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Fixed
 - Copy as Markdown of the [visualizer](https://webperf-snippets.net/visualizer) exported an audit that has a rating and no value, such as Script-Loading, as a metric: a heading with `undefined` and none of its issues or items, and nothing at all when its unit is a score. The export picks its format as the page picks its view, so the audit comes with its issues and its items, and a result the page shows as JSON is exported as JSON instead of "No issues found".
+- The panel of the extension stayed empty when the storage brought a theme or a side of the list that it does not know, such as a value synced from another version: it looked for the option of that value in the settings and stopped there. A saved value the panel does not know gives way to its default.
 
 ---
 
diff --git a/extension/lib/settings.js b/extension/lib/settings.js
index bd05ab34..468645bb 100644
--- a/extension/lib/settings.js
+++ b/extension/lib/settings.js
@@ -9,6 +9,20 @@
 export const DEFAULTS = { theme: 'devtools', side: 'left', sidebar: 'expanded', snippet: null, audits: [], reloadBeforeAudit: true, auditFilter: 'issues' }
 const SYNCED = new Set(['theme', 'side', 'reloadBeforeAudit', 'auditFilter'])
 
+// What each setting may hold. The storage can bring anything: a value of another version of the
+// extension, synced from another Chrome, or one written by hand. A value that fails gives way to
+// the default, so the panel never looks for a control that does not exist
+const oneOf = (...values) => (value) => values.includes(value)
+const VALID = {
+  theme: oneOf('devtools', 'light', 'dark'),
+  side: oneOf('left', 'right'),
+  sidebar: oneOf('expanded', 'collapsed'),
+  snippet: (value) => value === null || typeof value === 'string',
+  audits: Array.isArray,
+  reloadBeforeAudit: (value) => typeof value === 'boolean',
+  auditFilter: oneOf('errors', 'issues', 'all'),
+}
+
 export function createSettings(storage) {
   const areaOf = (key) => (SYNCED.has(key) ? storage?.sync : storage?.local)
   const read = async (area, keys) => {
@@ -25,7 +39,8 @@ export function createSettings(storage) {
         read(storage?.sync, keys.filter((k) => SYNCED.has(k))),
         read(storage?.local, keys.filter((k) => !SYNCED.has(k))),
       ])
-      return { ...DEFAULTS, ...synced, ...local }
+      const stored = { ...synced, ...local }
+      return Object.fromEntries(keys.map((key) => [key, key in stored && VALID[key](stored[key]) ? stored[key] : DEFAULTS[key]]))
     },
     async save(key, value) {
       try {
diff --git a/extension/lib/settings.test.js b/extension/lib/settings.test.js
index 0f245f43..0af96197 100644
--- a/extension/lib/settings.test.js
+++ b/extension/lib/settings.test.js
@@ -49,6 +49,18 @@ test('a value saved in the old place of the setting is ignored', async () => {
   assert.deepEqual(await settings.load(), DEFAULTS)
 })
 
+test('a saved value the panel does not know gives way to the default', async () => {
+  const sync = area({ theme: 'sepia', side: 'top', auditFilter: 'none', reloadBeforeAudit: 'yes' })
+  const local = area({ sidebar: 'floating', snippet: 42, audits: 'none' })
+  assert.deepEqual(await createSettings({ sync, local }).load(), DEFAULTS)
+})
+
+test('each value the panel knows is kept', async () => {
+  const sync = area({ theme: 'light', side: 'right', auditFilter: 'errors', reloadBeforeAudit: false })
+  const local = area({ sidebar: 'collapsed', snippet: 'LCP', audits: [] })
+  assert.deepEqual(await createSettings({ sync, local }).load(), { ...sync.data, ...local.data })
+})
+
 test('without chrome.storage, or when it fails, the panel keeps the defaults and saving does nothing', async () => {
   assert.deepEqual(await createSettings(undefined).load(), DEFAULTS)
   await createSettings(undefined).save('theme', 'dark')
diff --git a/extension/tests/panel.e2e.test.js b/extension/tests/panel.e2e.test.js
index 9f1e8680..a245255c 100644
--- a/extension/tests/panel.e2e.test.js
+++ b/extension/tests/panel.e2e.test.js
@@ -302,6 +302,25 @@ test('the settings choose the theme and the side of the list, and the panel reme
   assert.equal(await side(), 'left')
 })
 
+test('the panel opens with its defaults when the storage brings a theme or a side it does not know', async () => {
+  await panel.evaluate(() => {
+    localStorage.setItem('sync:theme', JSON.stringify('sepia'))
+    localStorage.setItem('sync:side', JSON.stringify('top'))
+  })
+  try {
+    await panel.reload()
+    await panel.waitForSelector('#list button', { timeout: 5000 })
+    await panel.click('#open-settings')
+    assert.ok(await panel.isChecked('input[name="theme"][value="devtools"]'))
+    assert.ok(await panel.isChecked('input[name="side"][value="left"]'))
+    await panel.click('#settings .close')
+  } finally {
+    // The page error of the panel that did not open is what the test reports, not the ones after it
+    await panel.evaluate(() => ['sync:theme', 'sync:side'].forEach((key) => localStorage.removeItem(key)))
+    await reopenPanel()
+  }
+})
+
 test('Clear empties the result, and only shows when there is one', async () => {
   await target.goto(`${servers.base}/seeded`, { waitUntil: 'load' })
   await panel.click('#list button[data-id="Input-Latency-Breakdown"]')