diff --git a/core/lib/Drupal/Core/Config/StorableConfigBase.php b/core/lib/Drupal/Core/Config/StorableConfigBase.php
index 5f5d007..a32087a 100644
--- a/core/lib/Drupal/Core/Config/StorableConfigBase.php
+++ b/core/lib/Drupal/Core/Config/StorableConfigBase.php
@@ -218,15 +218,13 @@ protected function castValue($key, $value) {
         $value[$nested_value_key] = $this->castValue($lookup_key, $nested_value);
       }
 
-      if ($element instanceof Mapping) {
+      // Only sort maps when we have more than 1 element to sort.
+      if ($element instanceof Mapping && count($value) > 1) {
         $mapping = $element->getDataDefinition()['mapping'];
-        // It is possible the schema is incomplete and the mapping not defined.
-        if (is_array($mapping)) {
-          // Only sort the keys in $value.
-          $mapping = array_intersect_key($mapping, $value);
-          // Sort the array in $value using the mapping definition.
-          $value = array_replace($mapping, $value);
-        }
+        // Only sort the keys in $value.
+        $mapping = array_intersect_key($mapping, $value);
+        // Sort the array in $value using the mapping definition.
+        $value = array_replace($mapping, $value);
       }
     }
     return $value;