diff --git a/core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php b/core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php
index c87193a2f0..55687bba3e 100644
--- a/core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php
+++ b/core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php
@@ -331,7 +331,10 @@ protected function loadFile($file)
             throw new InvalidArgumentException(sprintf('The service file "%s" is not valid.', $file));
         }
 
-        return $this->validate(Yaml::decode(file_get_contents($file)), $file);
+        // @todo Remove preg_replace() once
+        //   https://github.com/symfony/symfony/pull/25787 is in Symfony 3.4.
+        $content = preg_replace('/:$\n^\s+{\s*}$/m', ': {}', file_get_contents($file));
+        return $this->validate(Yaml::decode($content), $file);
     }
 
     /**
diff --git a/sites/default/default.services.yml b/sites/default/default.services.yml
index dd6d60e54e..e1bbbc7e21 100644
--- a/sites/default/default.services.yml
+++ b/sites/default/default.services.yml
@@ -126,13 +126,15 @@ parameters:
   # Not recommended in production environments
   # @default false
   http.response.debug_cacheability_headers: false
-  factory.keyvalue: {}
+  factory.keyvalue:
+    {}
     # Default key/value storage service to use.
     # @default keyvalue.database
     # default: keyvalue.database
     # Collection-specific overrides.
     # state: keyvalue.database
-  factory.keyvalue.expirable: {}
+  factory.keyvalue.expirable:
+    {}
     # Default key/value expirable storage service to use.
     # @default keyvalue.database.expirable
     # default: keyvalue.database.expirable