diff --git a/core/modules/language/migrations/d6_language_content_menu_settings.yml b/core/modules/language/migrations/d6_language_content_menu_settings.yml
index 12145c2d20..8e015f2182 100644
--- a/core/modules/language/migrations/d6_language_content_menu_settings.yml
+++ b/core/modules/language/migrations/d6_language_content_menu_settings.yml
@@ -4,7 +4,7 @@ migration_tags:
   - Drupal 6
   - Configuration
 source:
-  plugin: legacy_extension
+  plugin: extension
   name: i18nmenu
   constants:
     target_type: 'menu_link_content'
diff --git a/core/modules/system/src/Plugin/migrate/source/LegacyExtension.php b/core/modules/system/src/Plugin/migrate/source/Extension.php
similarity index 94%
rename from core/modules/system/src/Plugin/migrate/source/LegacyExtension.php
rename to core/modules/system/src/Plugin/migrate/source/Extension.php
index 02c4e5854a..379939110d 100644
--- a/core/modules/system/src/Plugin/migrate/source/LegacyExtension.php
+++ b/core/modules/system/src/Plugin/migrate/source/Extension.php
@@ -9,11 +9,11 @@
  * Gets system data for a legacy extension.
  *
  * @MigrateSource(
- *   id = "legacy_extension",
+ *   id = "extension",
  *   source_module = "system"
  * )
  */
-class LegacyExtension extends DrupalSqlBase {
+class Extension extends DrupalSqlBase {
 
   /**
    * {@inheritdoc}
diff --git a/core/modules/system/tests/src/Kernel/Plugin/migrate/source/LegacyExtensionTest.php b/core/modules/system/tests/src/Kernel/Plugin/migrate/source/ExtensionTest.php
similarity index 95%
rename from core/modules/system/tests/src/Kernel/Plugin/migrate/source/LegacyExtensionTest.php
rename to core/modules/system/tests/src/Kernel/Plugin/migrate/source/ExtensionTest.php
index 916fde56d1..1414dfc7ec 100644
--- a/core/modules/system/tests/src/Kernel/Plugin/migrate/source/LegacyExtensionTest.php
+++ b/core/modules/system/tests/src/Kernel/Plugin/migrate/source/ExtensionTest.php
@@ -7,10 +7,10 @@
 /**
  * Tests legacy extension source plugin.
  *
- * @covers \Drupal\system\Plugin\migrate\source\LegacyExtension
+ * @covers \Drupal\system\Plugin\migrate\source\Extension
  * @group migrate_drupal
  */
-class LegacyExtensionTest extends MigrateSqlSourceTestBase {
+class SourceLegacyExtensionTest extends MigrateSqlSourceTestBase {
 
   /**
    * {@inheritdoc}