diff --git a/lib/inlineattachmentlist.php b/lib/inlineattachmentlist.php
index 8b1a1cd9bb..de5008e87b 100644
--- a/lib/inlineattachmentlist.php
+++ b/lib/inlineattachmentlist.php
@@ -71,6 +71,17 @@ class InlineAttachmentListItem extends AttachmentListItem
         $this->out->elementEnd('a');
     }
 
+    /**
+     * Build HTML attributes for the link
+     * @return array
+     */
+    function linkAttr()
+    {
+        $attr = parent::linkAttr();
+        $attr['class'] = 'attachment-thumbnail';
+        return $attr;
+    }
+
     /**
      * start a single notice.
      *