diff --git a/js/src/forum/components/CommentPost.js b/js/src/forum/components/CommentPost.js
index be5dcda64..277fbdae4 100644
--- a/js/src/forum/components/CommentPost.js
+++ b/js/src/forum/components/CommentPost.js
@@ -51,7 +51,7 @@ export default class CommentPost extends Post {
         <ul>{listItems(this.headerItems().toArray())}</ul>
       </header>,
       <div className="Post-body">
-        {this.isEditing() ? <ComposerPostPreview composer={app.composer} /> : m.trust(this.attrs.post.contentHtml())}
+        {this.isEditing() ? <ComposerPostPreview className="Post-preview" composer={app.composer} /> : m.trust(this.attrs.post.contentHtml())}
       </div>,
     ]);
   }
diff --git a/js/src/forum/components/ComposerPostPreview.js b/js/src/forum/components/ComposerPostPreview.js
index 214f4ed9f..8c7a3c5c4 100644
--- a/js/src/forum/components/ComposerPostPreview.js
+++ b/js/src/forum/components/ComposerPostPreview.js
@@ -11,10 +11,15 @@ import Component from '../../common/Component';
  * ### Attrs
  *
  * - `composer` The state of the composer controlling this preview.
+ * - `className` A CSS class for the element surrounding the preview.
  */
 export default class ComposerPostPreview extends Component {
+  static initAttrs(attrs) {
+    attrs.className = attrs.className || '';
+  }
+
   view() {
-    return <div className="Post-preview" />;
+    return <div className={this.attrs.className} />;
   }
 
   oncreate(vnode) {