diff --git a/core/modules/filter/migration_templates/d6_filter_format.yml b/core/modules/filter/migration_templates/d6_filter_format.yml
index 6b767f2..a5f4388 100644
--- a/core/modules/filter/migration_templates/d6_filter_format.yml
+++ b/core/modules/filter/migration_templates/d6_filter_format.yml
@@ -16,11 +16,16 @@ process:
     key: '@id'
     process:
       id:
-        plugin: static_map
-        default_value: filter_null
+        # If the filter ID cannot be mapped, it will be passed through
+        # unchanged because the bypass flag is set. The filter_id plugin
+        # will flatten the input value and default it to filter_null (the
+        # fallback filter plugin ID) if the flattened input value is not
+        # a valid plugin ID.
+        plugin: filter_id
         source:
           - module
           - delta
+        bypass: true
         map:
           filter:
             - filter_html
diff --git a/core/modules/filter/migration_templates/d7_filter_format.yml b/core/modules/filter/migration_templates/d7_filter_format.yml
index 2b44a80..c0710b5 100644
--- a/core/modules/filter/migration_templates/d7_filter_format.yml
+++ b/core/modules/filter/migration_templates/d7_filter_format.yml
@@ -15,11 +15,16 @@ process:
     key: '@id'
     process:
       id:
-        plugin: static_map
+        # If the filter ID cannot be mapped, it will pass through unmodified
+        # because the bypass flag is set. When the user actually tries to
+        # view text through an invalid filter plugin, the filter system will
+        # fall back to filter_null and display a helpful error message.
+        plugin: filter_id
         bypass: true
         source: name
-        map:
-          php_code: filter_null
+        # No need to map anything -- filter plugin IDs haven't changed since
+        # Drupal 7.
+        map: { }
       settings:
         plugin: filter_settings
         source: settings
diff --git a/core/modules/filter/src/Plugin/migrate/process/FilterID.php b/core/modules/filter/src/Plugin/migrate/process/FilterID.php
new file mode 100644
index 0000000..2656986
--- /dev/null
+++ b/core/modules/filter/src/Plugin/migrate/process/FilterID.php
@@ -0,0 +1,90 @@
+<?php
+
+namespace Drupal\filter\Plugin\migrate\process;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\migrate\process\StaticMap;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * @MigrateProcessPlugin(
+ *   id = "filter_id"
+ * )
+ */
+class FilterID extends StaticMap implements ContainerFactoryPluginInterface {
+
+  /**
+   * The filter plugin manager.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface|\Drupal\Component\Plugin\FallbackPluginManagerInterface
+   */
+  protected $filterManager;
+
+  /**
+   * FilterID constructor.
+   *
+   * @param array $configuration
+   *   Plugin configuration.
+   * @param string $plugin_id
+   *   The plugin ID.
+   * @param mixed $plugin_definition
+   *   The plugin definition.
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $filter_manager
+   *   The filter plugin manager.
+   * @param TranslationInterface $translator
+   *   (optional) The string translation service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, PluginManagerInterface $filter_manager, TranslationInterface $translator = NULL) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->filterManager = $filter_manager;
+    $this->stringTranslation = $translator;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('plugin.manager.filter'),
+      $container->get('string_translation')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    $plugin_id = parent::transform($value, $migrate_executable, $row, $destination_property);
+
+    // If the static map is bypassed on failure, the returned plugin ID will be
+    // an array if $value was. Plugin IDs cannot be arrays, so flatten it before
+    // passing it into the filter manager.
+    if (is_array($plugin_id)) {
+      $plugin_id = implode(':', $plugin_id);
+    }
+
+    if ($this->filterManager->hasDefinition($plugin_id)) {
+      return $plugin_id;
+    }
+    else {
+      $fallback = $this->filterManager->getFallbackPluginId($plugin_id);
+
+      $message = $this->t('Filter @plugin_id could not be mapped to an existing filter plugin; defaulting to @fallback.', [
+        '@plugin_id' => $plugin_id,
+        '@fallback' => $fallback,
+      ]);
+      $migrate_executable->saveMessage((string) $message, MigrationInterface::MESSAGE_WARNING);
+
+      return $fallback;
+    }
+  }
+
+}
diff --git a/core/modules/filter/tests/src/Kernel/Migrate/d6/MigrateFilterFormatTest.php b/core/modules/filter/tests/src/Kernel/Migrate/d6/MigrateFilterFormatTest.php
index ed5f0fb..81faf3e 100644
--- a/core/modules/filter/tests/src/Kernel/Migrate/d6/MigrateFilterFormatTest.php
+++ b/core/modules/filter/tests/src/Kernel/Migrate/d6/MigrateFilterFormatTest.php
@@ -3,6 +3,7 @@
 namespace Drupal\Tests\filter\Kernel\Migrate\d6;
 
 use Drupal\filter\Entity\FilterFormat;
+use Drupal\filter\FilterFormatInterface;
 use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
 
 /**
@@ -39,14 +40,18 @@ public function testFilterFormat() {
     $this->assertFalse(isset($filters['filter_html_image_secure']));
 
     // Check variables migrated into filter.
-    $this->assertIdentical('<a href hreflang> <em> <strong> <cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd>', $filters['filter_html']['settings']['allowed_html']);
-    $this->assertIdentical(TRUE, $filters['filter_html']['settings']['filter_html_help']);
-    $this->assertIdentical(FALSE, $filters['filter_html']['settings']['filter_html_nofollow']);
-    $this->assertIdentical(72, $filters['filter_url']['settings']['filter_url_length']);
-
-    // Check that the PHP code filter is converted to filter_null.
-    $filters = FilterFormat::load('php_code')->get('filters');
-    $this->assertTrue(isset($filters['filter_null']));
+    $this->assertSame('<a href hreflang> <em> <strong> <cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd>', $filters['filter_html']['settings']['allowed_html']);
+    $this->assertSame(TRUE, $filters['filter_html']['settings']['filter_html_help']);
+    $this->assertSame(FALSE, $filters['filter_html']['settings']['filter_html_nofollow']);
+    $this->assertSame(72, $filters['filter_url']['settings']['filter_url_length']);
+
+    // Assert that the php_code format was migrated with filter_null in the
+    // php_code filter's place.
+    $filter_format = FilterFormat::load('php_code');
+    $this->assertInstanceOf(FilterFormatInterface::class, $filter_format);
+    $filters = $filter_format->get('filters');
+    $this->assertArrayHasKey('filter_null', $filters);
+    $this->assertArrayNotHasKey('php_code', $filters);
   }
 
 }
diff --git a/core/modules/filter/tests/src/Kernel/Migrate/d7/MigrateFilterFormatTest.php b/core/modules/filter/tests/src/Kernel/Migrate/d7/MigrateFilterFormatTest.php
index 8eb13b9..e4053ae 100644
--- a/core/modules/filter/tests/src/Kernel/Migrate/d7/MigrateFilterFormatTest.php
+++ b/core/modules/filter/tests/src/Kernel/Migrate/d7/MigrateFilterFormatTest.php
@@ -42,13 +42,13 @@ protected function setUp() {
   protected function assertEntity($id, $label, array $enabled_filters, $weight) {
     /** @var \Drupal\filter\FilterFormatInterface $entity */
     $entity = FilterFormat::load($id);
-    $this->assertTrue($entity instanceof FilterFormatInterface);
-    $this->assertIdentical($label, $entity->label());
+    $this->assertInstanceOf(FilterFormatInterface::class, $entity);
+    $this->assertSame($label, $entity->label());
     // get('filters') will return enabled filters only, not all of them.
-    $this->assertIdentical(array_keys($enabled_filters), array_keys($entity->get('filters')));
-    $this->assertIdentical($weight, $entity->get('weight'));
+    $this->assertSame(array_keys($enabled_filters), array_keys($entity->get('filters')));
+    $this->assertSame($weight, $entity->get('weight'));
     foreach ($entity->get('filters') as $filter_id => $filter) {
-      $this->assertIdentical($filter['weight'], $enabled_filters[$filter_id]);
+      $this->assertSame($filter['weight'], $enabled_filters[$filter_id]);
     }
   }
 
@@ -68,15 +68,17 @@ public function testFilterFormat() {
     // Ensure that filter-specific settings were migrated.
     /** @var \Drupal\filter\FilterFormatInterface $format */
     $format = FilterFormat::load('filtered_html');
+    $this->assertInstanceOf(FilterFormatInterface::class, $format);
     $config = $format->filters('filter_html')->getConfiguration();
-    $this->assertIdentical('<div> <span> <ul type> <li> <ol start type> <a href hreflang> <img src alt height width>', $config['settings']['allowed_html']);
+    $this->assertSame('<div> <span> <ul type> <li> <ol start type> <a href hreflang> <img src alt height width>', $config['settings']['allowed_html']);
     $config = $format->filters('filter_url')->getConfiguration();
-    $this->assertIdentical(128, $config['settings']['filter_url_length']);
+    $this->assertSame(128, $config['settings']['filter_url_length']);
 
     // The php_code format gets migrated, but the php_code filter is changed to
     // filter_null.
-    $filters = FilterFormat::load('php_code')->get('filters');
-    $this->assertTrue(isset($filters['filter_null']));
+    $format = FilterFormat::load('php_code');
+    $this->assertInstanceOf(FilterFormatInterface::class, $format);
+    $this->assertArrayHasKey('filter_null', $format->get('filters'));
   }
 
 }
diff --git a/core/modules/filter/tests/src/Kernel/Plugin/migrate/process/FilterIdTest.php b/core/modules/filter/tests/src/Kernel/Plugin/migrate/process/FilterIdTest.php
new file mode 100644
index 0000000..39e4037
--- /dev/null
+++ b/core/modules/filter/tests/src/Kernel/Plugin/migrate/process/FilterIdTest.php
@@ -0,0 +1,119 @@
+<?php
+
+namespace Drupal\Tests\filter\Kernel\Plugin\migrate\process;
+
+use Drupal\filter\Plugin\migrate\process\FilterID;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\Row;
+
+/**
+ * Unit tests of the filter_id plugin.
+ *
+ * @coversDefaultClass \Drupal\filter\Plugin\migrate\process\FilterID
+ * @group filter
+ */
+class FilterIdTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['filter'];
+
+  /**
+   * The mocked MigrateExecutable.
+   *
+   * @var MigrateExecutableInterface|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $executable;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->executable = $this->getMock(MigrateExecutableInterface::class);
+  }
+
+  /**
+   * Tests the filter_id plugin.
+   *
+   * @param mixed $value
+   *   The input value to the plugin.
+   * @param string $expected_value
+   *   The output value expected from the plugin.
+   * @param string $invalid_id
+   *   (optional) The invalid plugin ID which is expected to be logged by the
+   *   MigrateExecutable object.
+   *
+   * @dataProvider testProvider
+   *
+   * @covers ::transform
+   */
+  public function test($value, $expected_value, $invalid_id = NULL) {
+    $configuration = [
+      'bypass' => TRUE,
+      'map' => [
+        'foo' => 'filter_html',
+        'baz' => 'php_code',
+      ],
+    ];
+    $plugin = FilterID::create($this->container, $configuration, 'filter_id', []);
+
+    if (isset($invalid_id)) {
+      $this->executable
+        ->expects($this->exactly(1))
+        ->method('saveMessage')
+        ->with(
+          'Filter ' . $invalid_id . ' could not be mapped to an existing filter plugin; defaulting to filter_null.',
+          MigrationInterface::MESSAGE_WARNING
+        );
+    }
+
+    $row = new Row([], []);
+    $output_value = $plugin->transform($value, $this->executable, $row, 'foo');
+
+    $this->assertSame($expected_value, $output_value);
+  }
+
+  /**
+   * The test data provider.
+   *
+   * @return array
+   */
+  public function testProvider() {
+    return [
+      // The filter ID is mapped, and the plugin exists.
+      [
+        'foo',
+        'filter_html',
+      ],
+      // The filter ID isn't mapped, but it's unchanged from the source (i.e.,
+      // it bypasses the static map) and the plugin exists.
+      [
+        'filter_html',
+        'filter_html',
+      ],
+      // The filter ID is mapped, but the plugin does not exist.
+      [
+        'baz',
+        'filter_null',
+        'php_code',
+      ],
+      // The filter ID isn't mapped, but it's unchanged from the source (i.e.,
+      // it bypasses the static map) but the plugin does not exist.
+      [
+        'php_code',
+        'filter_null',
+        'php_code',
+      ],
+      [
+        ['filter', 1],
+        'filter_null',
+        'filter:1',
+      ],
+    ];
+  }
+
+}
diff --git a/core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserRoleTest.php b/core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserRoleTest.php
index f7613e2..d3f49cc 100644
--- a/core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserRoleTest.php
+++ b/core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserRoleTest.php
@@ -28,22 +28,22 @@ public function testUserRole() {
     $id_map = $this->getMigration('d6_user_role')->getIdMap();
     $rid = 'anonymous';
     $anonymous = Role::load($rid);
-    $this->assertIdentical($rid, $anonymous->id());
-    $this->assertIdentical(array('migrate test anonymous permission', 'use text format filtered_html'), $anonymous->getPermissions());
-    $this->assertIdentical(array($rid), $id_map->lookupDestinationId(array(1)));
+    $this->assertSame($rid, $anonymous->id());
+    $this->assertSame(array('migrate test anonymous permission', 'use text format filtered_html'), $anonymous->getPermissions());
+    $this->assertSame(array($rid), $id_map->lookupDestinationId(array(1)));
     $rid = 'authenticated';
     $authenticated = Role::load($rid);
-    $this->assertIdentical($rid, $authenticated->id());
-    $this->assertIdentical(array('migrate test authenticated permission', 'use text format filtered_html'), $authenticated->getPermissions());
-    $this->assertIdentical(array($rid), $id_map->lookupDestinationId(array(2)));
+    $this->assertSame($rid, $authenticated->id());
+    $this->assertSame(array('migrate test authenticated permission', 'use text format filtered_html'), $authenticated->getPermissions());
+    $this->assertSame(array($rid), $id_map->lookupDestinationId(array(2)));
     $rid = 'migrate_test_role_1';
     $migrate_test_role_1 = Role::load($rid);
-    $this->assertIdentical($rid, $migrate_test_role_1->id());
-    $this->assertIdentical(array('migrate test role 1 test permission', 'use text format full_html', 'use text format php_code'), $migrate_test_role_1->getPermissions());
-    $this->assertIdentical(array($rid), $id_map->lookupDestinationId(array(3)));
+    $this->assertSame($rid, $migrate_test_role_1->id());
+    $this->assertSame(array('migrate test role 1 test permission', 'use text format full_html', 'use text format php_code'), $migrate_test_role_1->getPermissions());
+    $this->assertSame(array($rid), $id_map->lookupDestinationId(array(3)));
     $rid = 'migrate_test_role_2';
     $migrate_test_role_2 = Role::load($rid);
-    $this->assertIdentical(array(
+    $this->assertSame(array(
       'migrate test role 2 test permission',
       'use PHP for settings',
       'administer contact forms',
@@ -61,12 +61,12 @@ public function testUserRole() {
       'access content overview',
       'use text format php_code',
       ), $migrate_test_role_2->getPermissions());
-    $this->assertIdentical($rid, $migrate_test_role_2->id());
-    $this->assertIdentical(array($rid), $id_map->lookupDestinationId(array(4)));
+    $this->assertSame($rid, $migrate_test_role_2->id());
+    $this->assertSame(array($rid), $id_map->lookupDestinationId(array(4)));
     $rid = 'migrate_test_role_3_that_is_long';
     $migrate_test_role_3 = Role::load($rid);
-    $this->assertIdentical($rid, $migrate_test_role_3->id());
-    $this->assertIdentical(array($rid), $id_map->lookupDestinationId(array(5)));
+    $this->assertSame($rid, $migrate_test_role_3->id());
+    $this->assertSame(array($rid), $id_map->lookupDestinationId(array(5)));
   }
 
 }