diff --git a/tests/browser/workspace-system.spec.mjs b/tests/browser/workspace-system.spec.mjs
index 5c55a938..1f56f989 100644
--- a/tests/browser/workspace-system.spec.mjs
+++ b/tests/browser/workspace-system.spec.mjs
@@ -650,14 +650,16 @@ test('server settings that cannot be read say so in their rows', async ({ page }
         ? route.fulfill({ status: 500, contentType: 'application/json', body: JSON.stringify({ success: false, error: 'Injected failure' }) })
         : route.continue()));
     await page.goto(`${workspace}#/system/appearance`);
-    for (const id of ['open-mode', 'timeout']) {
+    // #317: the Thumbnails rows are server settings too.
+    for (const id of ['open-mode', 'timeout', 'thumbnail-format', 'thumbnail-quality', 'thumbnail-edge']) {
         const row = page.locator('#workspace-main .setting-row').filter({ has: page.locator(`#${id}`) });
-        await expect(row.locator('p.small')).toHaveText('Server settings could not be read.');
+        await expect(row.locator('p.small').first()).toHaveText('Server settings could not be read.');
         await expect(page.locator(`#${id}`)).toBeDisabled();
     }
     // The browser rows are this browser's, and work as before.
     await expect(page.locator('#default-view')).toBeEnabled();
-    await expect(page.locator('#workspace-main .setting-row p.small')).toHaveCount(2);
+    await expect(page.locator('#workspace-main .setting-row p.small', { hasText: 'Server settings could not be read.' })).toHaveCount(5);
+    await expect(page.locator('#workspace-main section.surface').first().locator('.setting-row p.small')).toHaveCount(2);
 });
 
 test('stale revision shows the conflict status', async ({ page, request }) => {
diff --git a/tests/js/workspace-system-thumbnails.test.js b/tests/js/workspace-system-thumbnails.test.js
index 07d98ecf..e7169f11 100644
--- a/tests/js/workspace-system-thumbnails.test.js
+++ b/tests/js/workspace-system-thumbnails.test.js
@@ -67,7 +67,7 @@ const HOST = { thumbnail_format: 'webp', thumbnail_quality: 80, thumbnail_edge:
 const NO_JXL = { webp: { available: true }, jpeg: { available: true },
     jxl: { available: false, encoder: null, reason: 'No JPEG XL encoder found. Install pillow-jxl-plugin.' } };
 
-async function mounted({ host = HOST, browserJxl = true, writeHost = async () => ({ success: true, persisted: true, revision: 'sha256:two' }) } = {}) {
+async function mounted({ host = HOST, browserJxl = true, hostFails = false, writeHost = async () => ({ success: true, persisted: true, revision: 'sha256:two' }) } = {}) {
     const { mountThumbnailSettings } = await thumbnailsModule;
     const { createSystemDrafts } = await stateModule;
     const { createScope } = await coreModule;
@@ -75,7 +75,7 @@ async function mounted({ host = HOST, browserJxl = true, writeHost = async () =>
     let hostValues = null;
     const drafts = createSystemDrafts({
         readBrowser: () => ({}), readRuntime: () => ({}),
-        readHost: async () => ({ values: hostValues, revision: 'sha256:one' }),
+        readHost: async () => { if (hostFails) throw new Error('offline'); return { values: hostValues, revision: 'sha256:one' }; },
         writeBrowser: async () => ({ persisted: true }), writeHost, writeRuntime: async () => ({}),
     });
     const scope = createScope();
@@ -181,3 +181,15 @@ test('Convert outdated opens Thumbnail maintenance on its convert scope; a forma
         assert.equal(reviews.length, 1, 'nothing starts by itself');
     } finally { scope.dispose(); assert.equal(dom.listenerCount(), 0); dom.restore(); }
 });
+
+test('rows whose server settings could not be read say so, like Appearance’s host rows', async () => {
+    const { HOST_UNAVAILABLE } = await import('../../web/js/workspace/system-appearance.mjs');
+    const { dom, drafts, scope, surface, byId } = await mounted({ hostFails: true });
+    const notes = () => surface.children.slice(2, 5).map(row => row.children[0].children.slice(2).map(note => note.textContent));
+    try {
+        assert.deepEqual(notes(), [[], [], []]);
+        assert.equal(await drafts.reloadHost(), false);
+        assert.deepEqual(notes(), [[HOST_UNAVAILABLE], [HOST_UNAVAILABLE], [HOST_UNAVAILABLE]]);
+        for (const id of ['thumbnail-format', 'thumbnail-quality', 'thumbnail-edge']) assert.equal(byId(id).disabled, true, id);
+    } finally { scope.dispose(); assert.equal(dom.listenerCount(), 0); dom.restore(); }
+});
diff --git a/web/js/workspace/system-thumbnails.mjs b/web/js/workspace/system-thumbnails.mjs
index e51895e5..33b20b29 100644
--- a/web/js/workspace/system-thumbnails.mjs
+++ b/web/js/workspace/system-thumbnails.mjs
@@ -14,11 +14,13 @@
  *   automatic. After a save that changed the format, its line says existing previews keep their old format until
  *   converted.
  *
- * Host rows stay disabled until the server settings were read, like Appearance's.
+ * Host rows stay disabled until the server settings were read, like Appearance's, and say "Server settings could not
+ * be read." while a read failed.
  */
 import { settingRow, operationRow } from './system-controls.mjs';
 import { detectJxlSupport } from './thumbnail-support.mjs';
 import { openThumbnailReview } from './thumbnail-review.mjs';
+import { HOST_UNAVAILABLE } from './system-appearance.mjs';
 
 export const FORMAT_OPTIONS = Object.freeze([['webp', 'WebP'], ['jxl', 'JPEG XL'], ['jpeg', 'JPEG']]);
 export const QUALITY_LIMIT = Object.freeze({ min: 1, max: 100 });
@@ -84,7 +86,6 @@ export function mountThumbnailSettings(container, { scope, drafts, api, activity
     let browserJxl;
     let savedFormat;
     const format = controls[0];
-    const notes = [];
     const repaint = () => {
         const encoders = drafts.get('host', 'thumbnail_encoders');
         for (const { input, key } of controls) {
@@ -95,12 +96,13 @@ export function mountThumbnailSettings(container, { scope, drafts, api, activity
         const jxl = Array.from(format.input.children).find(option => option.value === 'jxl');
         const unavailable = encoders?.jxl?.available === false;
         if (jxl) jxl.disabled = unavailable;
-        for (const note of notes.splice(0)) note.remove();
-        const lines = [unavailable ? encoders.jxl.reason : null, browserJxl === false ? BROWSER_NO_JXL : null];
-        for (const line of lines.filter(Boolean)) {
-            const note = el('p', line, 'small');
-            format.text.append(note);
-            notes.push(note);
+        const failed = drafts.hostState?.() === 'failed';
+        for (const row of controls) {
+            for (const note of row.notes ?? []) note.remove();
+            const lines = [failed && drafts.get('host', row.key) === undefined ? HOST_UNAVAILABLE : null];
+            if (row === format) lines.push(unavailable ? encoders.jxl.reason : null, browserJxl === false ? BROWSER_NO_JXL : null);
+            row.notes = lines.filter(Boolean).map(line => el('p', line, 'small'));
+            row.text.append(...row.notes);
         }
         // A format save (not the first read) leaves the existing previews outdated: say so, never convert.
         const saved = drafts.saved('host').thumbnail_format;