diff --git a/core/modules/content_translation/migrations/d6_custom_block_translation.yml b/core/modules/content_translation/migrations/d6_custom_block_translation.yml
index dda0409319..7fe330a9f2 100644
--- a/core/modules/content_translation/migrations/d6_custom_block_translation.yml
+++ b/core/modules/content_translation/migrations/d6_custom_block_translation.yml
@@ -8,11 +8,11 @@ source:
   plugin: d6_box_translation
 process:
   id:
-    plugin: migration_lookup
-    migration: d6_custom_block
-    source:
-      - bid
-    return_associative: TRUE
+    -
+      plugin: migration_lookup
+      migration: d6_custom_block
+      source: bid
+      return_associative: TRUE
     -
       plugin: extract
       index: