diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Comment.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Comment.php
index 7ae2aa8..5726da6 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Comment.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Comment.php
@@ -35,7 +35,7 @@ public function query() {
   /**
    * {@inheritdoc}
    */
-  public function prepareRow(Row $row, $keep = TRUE) {
+  public function prepareRow(Row $row) {
     // In D6, status=0 means published, while in D8 means the opposite.
     // See https://drupal.org/node/237636
     $row->setSourceProperty('status', !$row->getSourceProperty('status'));
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Field.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Field.php
index 542fde2..3738dce 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Field.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Field.php
@@ -68,7 +68,7 @@ public function fields() {
   /**
    * {@inheritdoc}
    */
-  public function prepareRow(Row $row, $keep = TRUE) {
+  public function prepareRow(Row $row) {
     // Unserialize data.
     $global_settings = unserialize($row->getSourceProperty('global_settings'));
     $widget_settings = unserialize($row->getSourceProperty('widget_settings'));
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/FieldInstance.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/FieldInstance.php
index e6f4721..35d2ecf 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/FieldInstance.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/FieldInstance.php
@@ -72,7 +72,7 @@ public function fields() {
   /**
    * {@inheritdoc}
    */
-  public function prepareRow(Row $row, $keep = TRUE) {
+  public function prepareRow(Row $row) {
     // Unserialize data.
     $widget_settings = unserialize($row->getSourceProperty('widget_settings'));
     $display_settings = unserialize($row->getSourceProperty('display_settings'));
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Role.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Role.php
index 754d6cd..5ba763f 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Role.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/Role.php
@@ -67,7 +67,7 @@ protected function runQuery() {
   /**
    * {@inheritdoc}
    */
-  public function prepareRow(Row $row, $keep = TRUE) {
+  public function prepareRow(Row $row) {
     $rid = $row->getSourceProperty('rid');
     $permissions = $this->select('permission', 'p')
       ->fields('p', array('perm'))
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/User.php b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/User.php
index 058f7ed..333765a 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/User.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/source/d6/User.php
@@ -52,7 +52,7 @@ public function fields() {
   /**
    * {@inheritdoc}
    */
-  public function prepareRow(Row $row, $keep = TRUE) {
+  public function prepareRow(Row $row) {
     // User roles.
     $roles = $this->select('users_roles', 'ur')
       ->fields('ur', array('rid'))