diff -u b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
--- b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/Entity.php
@@ -170,7 +170,11 @@
     $entity_id = reset($old_destination_id_values) ?: $this->getEntityId($row);
     if (!empty($entity_id) && ($entity = $this->storage->load($entity_id))) {
       // Allow updateEntity() to change the entity.
-      $this->updateEntity($entity, $row);
+      $result = $this->updateEntity($entity, $row);
+      if ($result !== NULL) {
+        trigger_error(__CLASS__ . '::updateEntity() should not return an entity. See https://www.drupal.org/project/drupal/issues/2921661');
+        $entity = $result;
+      }
     }
     else {
       // Attempt to ensure we always have a bundle.
diff -u b/core/modules/migrate/src/Plugin/migrate/destination/EntityContentBase.php b/core/modules/migrate/src/Plugin/migrate/destination/EntityContentBase.php
--- b/core/modules/migrate/src/Plugin/migrate/destination/EntityContentBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityContentBase.php
@@ -208,7 +208,8 @@
    *   The row object to update from.
    *
    * @return \Drupal\Core\Entity\EntityInterface
-   *   An updated entity from row values.
+   *   An updated entity from row values. This deprecated in Drupal 8.6.0 and
+   *   will be removed in Drupal 9. See tbd.
    */
   protected function updateEntity(EntityInterface &$entity, Row $row) {
     $empty_destinations = $row->getEmptyDestinationProperties();
diff -u b/core/modules/migrate/src/Plugin/migrate/destination/EntityRevision.php b/core/modules/migrate/src/Plugin/migrate/destination/EntityRevision.php
--- b/core/modules/migrate/src/Plugin/migrate/destination/EntityRevision.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityRevision.php
@@ -162,7 +162,11 @@
     }
     // We need to update the entity, so that the destination row IDs are
     // correct.
-    $this->updateEntity($entity, $row);
+    $result = $this->updateEntity($entity, $row);
+    if ($result !== NULL) {
+      trigger_error(__CLASS__ . '::updateEntity() should not return an entity. See https://www.drupal.org/project/drupal/issues/2921661');
+      $entity = $result;
+    }
     $entity->isDefaultRevision(FALSE);
     return $entity;
   }
interdiff impossible; taking evasive action
reverted:
--- b/core/modules/migrate/tests/src/Unit/Plugin/migrate/destination/EntityRevisionTest.php
+++ /dev/null
@@ -1,162 +0,0 @@
-<?php
-
-namespace Drupal\Tests\migrate\Unit\Plugin\migrate\destination;
-
-use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Entity\EntityStorageInterface;
-use Drupal\Core\Entity\EntityTypeInterface;
-use Drupal\Core\Field\BaseFieldDefinition;
-use Drupal\Core\Field\FieldTypePluginManagerInterface;
-use Drupal\migrate\MigrateException;
-use Drupal\migrate\Plugin\MigrationInterface;
-use Drupal\migrate\Plugin\migrate\destination\EntityRevision;
-use Drupal\migrate\Row;
-use Drupal\Tests\UnitTestCase;
-
-/**
- * Tests entity revision destination functionality.
- *
- * @coversDefaultClass \Drupal\migrate\Plugin\migrate\destination\EntityRevision
- * @group migrate
- */
-class EntityRevisionTest extends UnitTestCase {
-
-  /**
-   * The migration.
-   *
-   * @var \Drupal\migrate\Plugin\MigrationInterface
-   */
-  protected $migration;
-
-  /**
-   * The entity storage.
-   *
-   * @var \Drupal\Core\Entity\EntityStorageInterface
-   */
-  protected $storage;
-
-  /**
-   * The entity type.
-   *
-   * @var \Drupal\Core\Entity\EntityTypeInterface
-   */
-  protected $entityType;
-
-  /**
-   * The entity manager.
-   *
-   * @var \Drupal\Core\Entity\EntityManagerInterface
-   */
-  protected $entityManager;
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    $this->migration = $this->prophesize(MigrationInterface::class);
-    $this->storage = $this->prophesize(EntityStorageInterface::class);
-
-    $this->entityType = $this->prophesize(EntityTypeInterface::class);
-    $this->entityType->getSingularLabel()->willReturn('foo');
-    $this->entityType->getPluralLabel()->willReturn('bar');
-    $this->storage->getEntityType()->willReturn($this->entityType->reveal());
-    $this->storage->getEntityTypeId()->willReturn('foo');
-
-    $this->entityManager = $this->prophesize(EntityManagerInterface::class);
-  }
-
-  /**
-   * Tests that revision destination fails for unrevisionable entities.
-   */
-  public function testUnrevisionable() {
-    $this->entityType->getKey('id')->willReturn('id');
-    $this->entityType->getKey('revision')->willReturn('');
-    $this->entityManager->getBaseFieldDefinitions('foo')
-      ->willReturn([
-        'id' => BaseFieldDefinitionTest::create('integer'),
-      ]);
-
-    $destination = new EntityRevisionTestDestination(
-      [],
-      '',
-      [],
-      $this->migration->reveal(),
-      $this->storage->reveal(),
-      [],
-      $this->entityManager->reveal(),
-      $this->prophesize(FieldTypePluginManagerInterface::class)->reveal()
-    );
-    $this->setExpectedException(MigrateException::class, 'The "foo" entity type does not support revisions.');
-    $destination->getIds();
-  }
-
-  /**
-   * Tests that translation destination fails for untranslatable entities.
-   */
-  public function testUntranslatable() {
-    $this->entityType->getKey('id')->willReturn('id');
-    $this->entityType->getKey('revision')->willReturn('vid');
-    $this->entityType->getKey('langcode')->willReturn('');
-    $this->entityManager->getBaseFieldDefinitions('foo')
-      ->willReturn([
-        'id' => BaseFieldDefinitionTest::create('integer'),
-        'vid' => BaseFieldDefinitionTest::create('integer'),
-      ]);
-
-    $destination = new EntityRevisionTestDestination(
-      ['translations' => TRUE],
-      '',
-      [],
-      $this->migration->reveal(),
-      $this->storage->reveal(),
-      [],
-      $this->entityManager->reveal(),
-      $this->prophesize(FieldTypePluginManagerInterface::class)->reveal()
-    );
-    $this->setExpectedException(MigrateException::class, 'The "foo" entity type does not support translations.');
-    $destination->getIds();
-  }
-
-}
-
-/**
- * Stub class for testing EntityRevision methods.
- */
-class EntityRevisionTestDestination extends EntityRevision {
-
-  private $entity = NULL;
-
-  public function setEntity($entity) {
-    $this->entity = $entity;
-  }
-
-  protected function getEntity(Row $row, array $old_destination_id_values) {
-    return $this->entity;
-  }
-
-  public static function getEntityTypeId($plugin_id) {
-    return 'foo';
-  }
-
-}
-
-/**
- * Stub class for BaseFieldDefinition.
- */
-class BaseFieldDefinitionTest extends BaseFieldDefinition {
-
-  public static function create($type) {
-    return new static([]);
-  }
-
-  public function getSettings() {
-    return [];
-  }
-
-  public function getType() {
-    return 'integer';
-  }
-
-}
unchanged:
--- a/core/modules/migrate/tests/src/Unit/Plugin/migrate/destination/EntityContentBaseTest.php
+++ b/core/modules/migrate/tests/src/Unit/Plugin/migrate/destination/EntityRevisionTest.php
@@ -1,13 +1,7 @@
 <?php
 
-/**
- * @file
- * Contains \Drupal\Tests\migrate\Unit\Plugin\migrate\destination\EntityContentBaseTest
- */
-
 namespace Drupal\Tests\migrate\Unit\Plugin\migrate\destination;
 
-use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
@@ -15,35 +9,42 @@
 use Drupal\Core\Field\FieldTypePluginManagerInterface;
 use Drupal\migrate\MigrateException;
 use Drupal\migrate\Plugin\MigrationInterface;
-use Drupal\migrate\Plugin\migrate\destination\EntityContentBase;
-use Drupal\migrate\Plugin\MigrateIdMapInterface;
+use Drupal\migrate\Plugin\migrate\destination\EntityRevision;
 use Drupal\migrate\Row;
 use Drupal\Tests\UnitTestCase;
 
 /**
- * Tests base entity migration destination functionality.
+ * Tests entity revision destination functionality.
  *
- * @coversDefaultClass \Drupal\migrate\Plugin\migrate\destination\EntityContentBase
+ * @coversDefaultClass \Drupal\migrate\Plugin\migrate\destination\EntityRevision
  * @group migrate
  */
-class EntityContentBaseTest extends UnitTestCase {
+class EntityRevisionTest extends UnitTestCase {
 
   /**
+   * The migration.
+   *
    * @var \Drupal\migrate\Plugin\MigrationInterface
    */
   protected $migration;
 
   /**
+   * The entity storage.
+   *
    * @var \Drupal\Core\Entity\EntityStorageInterface
    */
   protected $storage;
 
   /**
+   * The entity type.
+   *
    * @var \Drupal\Core\Entity\EntityTypeInterface
    */
   protected $entityType;
 
   /**
+   * The entity manager.
+   *
    * @var \Drupal\Core\Entity\EntityManagerInterface
    */
   protected $entityManager;
@@ -58,68 +59,53 @@ protected function setUp() {
     $this->storage = $this->prophesize(EntityStorageInterface::class);
 
     $this->entityType = $this->prophesize(EntityTypeInterface::class);
-    $this->entityType->getPluralLabel()->willReturn('wonkiness');
+    $this->entityType->getSingularLabel()->willReturn('foo');
+    $this->entityType->getPluralLabel()->willReturn('bar');
     $this->storage->getEntityType()->willReturn($this->entityType->reveal());
+    $this->storage->getEntityTypeId()->willReturn('foo');
 
     $this->entityManager = $this->prophesize(EntityManagerInterface::class);
   }
 
   /**
-   * Test basic entity save.
-   *
-   * @covers ::import
+   * Tests that revision destination fails for unrevisionable entities.
    */
-  public function testImport() {
-    $bundles = [];
-    $destination = new EntityTestDestination([], '', [],
-      $this->migration->reveal(),
-      $this->storage->reveal(),
-      $bundles,
-      $this->entityManager->reveal(),
-      $this->prophesize(FieldTypePluginManagerInterface::class)->reveal());
-    $entity = $this->prophesize(ContentEntityInterface::class);
-    // Assert that save is called.
-    $entity->save()
-      ->shouldBeCalledTimes(1);
-    // Set an id for the entity
-    $entity->id()
-      ->willReturn(5);
-    $destination->setEntity($entity->reveal());
-    // Ensure the id is saved entity id is returned from import.
-    $this->assertEquals([5], $destination->import(new Row()));
-    // Assert that import set the rollback action.
-    $this->assertEquals(MigrateIdMapInterface::ROLLBACK_DELETE, $destination->rollbackAction());
-  }
+  public function testUnrevisionable() {
+    $this->entityType->getKey('id')->willReturn('id');
+    $this->entityType->getKey('revision')->willReturn('');
+    $this->entityManager->getBaseFieldDefinitions('foo')
+      ->willReturn([
+        'id' => BaseFieldDefinitionTest::create('integer'),
+      ]);
 
-  /**
-   * Test row skipping when we can't get an entity to save.
-   *
-   * @covers ::import
-   */
-  public function testImportEntityLoadFailure() {
-    $bundles = [];
-    $destination = new EntityTestDestination([], '', [],
+    $destination = new EntityRevisionTestDestination(
+      [],
+      '',
+      [],
       $this->migration->reveal(),
       $this->storage->reveal(),
-      $bundles,
+      [],
       $this->entityManager->reveal(),
-      $this->prophesize(FieldTypePluginManagerInterface::class)->reveal());
-    $destination->setEntity(FALSE);
-    $this->setExpectedException(MigrateException::class, 'Unable to get entity');
-    $destination->import(new Row());
+      $this->prophesize(FieldTypePluginManagerInterface::class)->reveal()
+    );
+    $this->setExpectedException(MigrateException::class, 'The "foo" entity type does not support revisions.');
+    $destination->getIds();
   }
 
   /**
-   * Test that translation destination fails for untranslatable entities.
+   * Tests that translation destination fails for untranslatable entities.
    */
   public function testUntranslatable() {
-    // An entity type without a language.
-    $this->entityType->getKey('langcode')->willReturn('');
     $this->entityType->getKey('id')->willReturn('id');
+    $this->entityType->getKey('revision')->willReturn('vid');
+    $this->entityType->getKey('langcode')->willReturn('');
     $this->entityManager->getBaseFieldDefinitions('foo')
-      ->willReturn(['id' => BaseFieldDefinitionTest::create('integer')]);
+      ->willReturn([
+        'id' => BaseFieldDefinitionTest::create('integer'),
+        'vid' => BaseFieldDefinitionTest::create('integer'),
+      ]);
 
-    $destination = new EntityTestDestination(
+    $destination = new EntityRevisionTestDestination(
       ['translations' => TRUE],
       '',
       [],
@@ -129,18 +115,16 @@ public function testUntranslatable() {
       $this->entityManager->reveal(),
       $this->prophesize(FieldTypePluginManagerInterface::class)->reveal()
     );
-    $this->setExpectedException(MigrateException::class, 'This entity type does not support translation');
+    $this->setExpectedException(MigrateException::class, 'The "foo" entity type does not support translations.');
     $destination->getIds();
   }
 
 }
 
 /**
- * Stub class for testing EntityContentBase methods.
- *
- * We want to test things without testing the base class implementations.
+ * Stub class for testing EntityRevision methods.
  */
-class EntityTestDestination extends EntityContentBase {
+class EntityRevisionTestDestination extends EntityRevision {
 
   private $entity = NULL;
 
diff -u b/core/modules/migrate/tests/src/Unit/destination/EntityRevisionTest.php b/core/modules/migrate/tests/src/Unit/destination/EntityRevisionTest.php
--- b/core/modules/migrate/tests/src/Unit/destination/EntityRevisionTest.php
+++ b/core/modules/migrate/tests/src/Unit/destination/EntityRevisionTest.php
@@ -231,7 +231,5 @@
    * empty implementation avoids this.
    */
-  protected function updateEntity(EntityInterface &$entity, Row $row) {
-    return $entity;
-  }
+  protected function updateEntity(EntityInterface &$entity, Row $row) {}
 
 }
only in patch2:
unchanged:
--- a/core/modules/migrate/src/Plugin/migrate/destination/EntityConfigBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityConfigBase.php
@@ -186,12 +186,14 @@ public function getIds() {
   /**
    * Updates an entity with the contents of a row.
    *
+   * Note that the entity passed in is updated.
+   *
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   The entity to update.
    * @param \Drupal\migrate\Row $row
    *   The row object to update from.
    */
-  protected function updateEntity(EntityInterface $entity, Row $row) {
+  protected function updateEntity(EntityInterface &$entity, Row $row) {
     // This is a translation if the language in the active config does not
     // match the language of this row.
     $translation = FALSE;
only in patch2:
unchanged:
--- a/core/modules/search/src/Plugin/migrate/destination/EntitySearchPage.php
+++ b/core/modules/search/src/Plugin/migrate/destination/EntitySearchPage.php
@@ -21,7 +21,7 @@ class EntitySearchPage extends EntityConfigBase {
    * @param \Drupal\migrate\Row $row
    *   The row object to update from.
    */
-  protected function updateEntity(EntityInterface $entity, Row $row) {
+  protected function updateEntity(EntityInterface &$entity, Row $row) {
     $entity->setPlugin($row->getDestinationProperty('plugin'));
     $entity->getPlugin()->setConfiguration($row->getDestinationProperty('configuration'));
   }