diff -u b/core/modules/content_translation/src/Plugin/migrate/source/d6/BlockTranslation.php b/core/modules/content_translation/src/Plugin/migrate/source/d6/BlockTranslation.php
--- b/core/modules/content_translation/src/Plugin/migrate/source/d6/BlockTranslation.php
+++ b/core/modules/content_translation/src/Plugin/migrate/source/d6/BlockTranslation.php
@@ -10,7 +10,7 @@
  *
  * @MigrateSource(
  *   id = "d6_block_translation",
- *   source_provider = "block"
+ *   source_module = "block"
  * )
  */
 class BlockTranslation extends DrupalSqlBase {
diff -u b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php
--- b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php
+++ b/core/modules/content_translation/src/Plugin/migrate/source/d6/BoxTranslation.php
@@ -10,7 +10,8 @@
  * Gets Drupal 6 i18n custom block translations from database.
  *
  * @MigrateSource(
- *   id = "d6_box_translation"
+ *   id = "d6_box_translation",
+ *   source_module = "boxes"
  * )
  */
 class BoxTranslation extends DrupalSqlBase {