diff --git a/core/modules/field/src/Entity/FieldConfig.php b/core/modules/field/src/Entity/FieldConfig.php
index fe74bf4..e56aa06 100644
--- a/core/modules/field/src/Entity/FieldConfig.php
+++ b/core/modules/field/src/Entity/FieldConfig.php
@@ -469,7 +469,7 @@ public function getSchema() {
 
       // Merge custom indexes with those specified by the field type. Custom
       // indexes prevail.
-      $schema['indexes'] = $this->getIndexes() + $schema['indexes'];
+      $schema['indexes'] = $this->indexes + $schema['indexes'];
 
       $this->schema = $schema;
     }