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
@@ -27,7 +27,7 @@
       ->fields('b', ['bid', 'module', 'delta', 'theme', 'title']);
     $query->addField('b', 'module', 'block_module');
     $query->addField('b', 'delta', 'block_delta');
-    $query->innerJoin($this->blockTable, 'b', ('b.module = i18n.module AND b.delta = i18n.delta'));
+    $query->leftJoin($this->blockTable, 'b', ('b.module = i18n.module AND b.delta = i18n.delta'));
     return $query;
   }