diff --git a/core/lib/Drupal/Component/Yaml/Yaml.php b/core/lib/Drupal/Component/Yaml/Yaml.php
index c016f69..ee759b2 100644
--- a/core/lib/Drupal/Component/Yaml/Yaml.php
+++ b/core/lib/Drupal/Component/Yaml/Yaml.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\Component\Yaml;
+use Drupal\Component\Utility\Settings;
 
 /**
  * Factory class for YAML parsing.
@@ -65,8 +66,12 @@ protected function determineImplementation() {
       return static::$implementationClass;
     }
 
+    // If there's a settings.php override, use that.
+    if ($class = Settings::getSingleton()->get('yaml_parser_class')) {
+      static::$implementationClass = $class;
+    }
     // If the PECL YAML extension installed, use that.
-    if (function_exists('yaml_emit')) {
+    elseif (function_exists('yaml_emit')) {
       static::$implementationClass = 'Drupal\Component\Yaml\Pecl';
     }
     else {