diff --git a/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php b/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php
index fb1742b..63dd984 100644
--- a/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php
+++ b/core/modules/comment/src/Plugin/migrate/source/d6/Comment.php
@@ -34,8 +34,18 @@ public function query() {
    * {@inheritdoc}
    */
   public function prepareRow(Row $row) {
-    // This is a backward compatibility layer for the deprecated migrate source
-    // plugins d6_comment_variable and d6_comment_variable_per_comment_type.
+    return parent::prepareRow($this->prepareComment($row));
+  }
+
+  /**
+   * This is a backward compatibility layer for the deprecated migrate source
+   * plugins d6_comment_variable and d6_comment_variable_per_comment_type.
+   *
+   * @deprecated in Drupal 8.4.x, to be removed before Drupal 9.0.x.
+   * @param \Drupal\migrate\Row $row
+   * @return \Drupal\migrate\Row
+   */
+  protected function prepareComment(Row $row) {
     if ($this->variableGet('comment_subject_field_' . $row->getSourceProperty('type'), 1)) {
       // Comment subject visible.
       $row->setSourceProperty('field_name', 'comment');
@@ -49,7 +59,7 @@ public function prepareRow(Row $row) {
     // In D6, status=0 means published, while in D8 means the opposite.
     // See https://www.drupal.org/node/237636.
     $row->setSourceProperty('status', !$row->getSourceProperty('status'));
-    return parent::prepareRow($row);
+    return $row;
   }
 
   /**