diff --git a/extensions/likes/js/src/forum/components/PostLikedNotification.js b/extensions/likes/js/src/forum/components/PostLikedNotification.js
index a9d16c2c11..78ddb6dda2 100644
--- a/extensions/likes/js/src/forum/components/PostLikedNotification.js
+++ b/extensions/likes/js/src/forum/components/PostLikedNotification.js
@@ -19,6 +19,6 @@ export default class PostLikedNotification extends Notification {
   }
 
   excerpt() {
-    return truncate(this.attrs.notification.subject().contentPlain(), 200);
+    return truncate(this.attrs.notification.subject().contentPlain() || '', 200);
   }
 }
diff --git a/extensions/likes/js/tests/unit/forum/PostLikedNotification.test.ts b/extensions/likes/js/tests/unit/forum/PostLikedNotification.test.ts
new file mode 100644
index 0000000000..c6531b6747
--- /dev/null
+++ b/extensions/likes/js/tests/unit/forum/PostLikedNotification.test.ts
@@ -0,0 +1,69 @@
+import bootstrapForum from '@flarum/jest-config/src/bootstrap/forum';
+import app from 'flarum/forum/app';
+import Notification from 'flarum/common/models/Notification';
+import PostLikedNotification from '../../../src/forum/components/PostLikedNotification';
+
+beforeAll(() => {
+  bootstrapForum();
+  app.boot();
+
+  // jsdom has no innerText, which a post's plain content is read from.
+  if (!('innerText' in HTMLElement.prototype)) {
+    Object.defineProperty(HTMLElement.prototype, 'innerText', {
+      get(this: HTMLElement) {
+        return this.textContent;
+      },
+    });
+  }
+
+  app.store.pushPayload({
+    data: { type: 'discussions', id: '1', attributes: { slug: '1-a-discussion', title: 'A discussion' } },
+  } as any);
+});
+
+function likedNotification(post: { id: string; attributes: Record<string, unknown> }) {
+  app.store.pushPayload({
+    data: { type: 'posts', ...post, relationships: { discussion: { data: { type: 'discussions', id: '1' } } } },
+  } as any);
+
+  return new Notification(
+    {
+      id: post.id,
+      type: 'notifications',
+      attributes: { contentType: 'postLiked', content: null, createdAt: new Date(), isRead: false },
+      relationships: { subject: { data: { type: 'posts', id: post.id } } },
+    },
+    app.store
+  );
+}
+
+/** What the notification renders, as it appears in the notification list. */
+function render(notification: Notification) {
+  const root = document.createElement('div');
+
+  m.render(root, m(PostLikedNotification, { notification }));
+
+  return root.querySelector('.Notification');
+}
+
+describe('the post liked notification', () => {
+  it('shows an excerpt of a liked comment', () => {
+    const notification = likedNotification({
+      id: '10',
+      attributes: { number: 2, contentType: 'comment', contentHtml: '<p>The liked comment</p>' },
+    });
+
+    expect(render(notification)?.textContent).toContain('The liked comment');
+  });
+
+  // The API accepts a like on any post type, and other types have no text. A
+  // notification that can't render takes the whole notification list with it.
+  it('renders for a liked post that has no text', () => {
+    const notification = likedNotification({
+      id: '11',
+      attributes: { number: 3, contentType: 'discussionRenamed', content: ['Old title', 'New title'] },
+    });
+
+    expect(render(notification)).not.toBeNull();
+  });
+});