diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index 696d103..71a7440 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -211,7 +211,7 @@ public function get() {
       $this->registry = $cache->data;
     }
     else {
-      if (lock()->acquire('theme_registry_build')) {
+      if ($this->lock->acquire('theme_registry_build')) {
         $this->registry = $this->build();
       }
       // Only persist it if all modules are loaded to ensure it is complete.
@@ -348,7 +348,7 @@ protected function build() {
     }
     $this->registry = $cache;
 
-    lock()->release('theme_registry_build');
+    $this->lock->release('theme_registry_build');
     return $this->registry;
   }