diff --git a/src/Base/ElasticPress/ElasticPress.php b/src/Base/ElasticPress/ElasticPress.php
index 355e298..a9e47f0 100644
--- a/src/Base/ElasticPress/ElasticPress.php
+++ b/src/Base/ElasticPress/ElasticPress.php
@@ -232,20 +232,19 @@ protected function formatOutputForElasticsearch(array $item): array
      */
     public function addMappings(array $mapping): array
     {
-        $mapping['mappings']['properties'] = [
-            'expired' => [
-                'type'       => 'object',
-                'properties' => [
-                    'on' => [
-                        'type'    => 'object',
-                        'enabled' => 'false'
-                    ]
+        $mapping['mappings']['properties']['expired'] = [
+            'type'       => 'object',
+            'properties' => [
+                'on' => [
+                    'type'    => 'object',
+                    'enabled' => 'false'
                 ]
             ],
-            'post_date_gmt'         => [
-                'type'   => 'date',
-                'format' => 'yyyy-MM-dd HH:mm:ss',
-            ],
+        ];
+
+        $mapping['mappings']['properties']['post_date_gmt'] = [
+            'type'   => 'date',
+            'format' => 'yyyy-MM-dd HH:mm:ss',
         ];
 
         return $mapping;