diff --git a/plugin.php b/plugin.php
index f2d8fde0..885e2f2e 100644
--- a/plugin.php
+++ b/plugin.php
@@ -491,7 +491,7 @@ protected function generate_graphql_block_type($block_type)
                 $union_type_name =
                     self::format_graphql_attributes_type_name($name) . 'Union';
                 register_graphql_union_type($union_type_name, [
-                    'types' => $attributes_types,
+                    'typeNames' => $attributes_types,
                     'resolveType' => function ($value) {
                         return $this->type_registry->get_type($value['__typename']);
                     }