diff --git a/core/lib/Drupal/Core/Routing/RouteProvider.php b/core/lib/Drupal/Core/Routing/RouteProvider.php
index 10c717e..c064622 100644
--- a/core/lib/Drupal/Core/Routing/RouteProvider.php
+++ b/core/lib/Drupal/Core/Routing/RouteProvider.php
@@ -58,7 +58,7 @@ class RouteProvider implements RouteProviderInterface, PagedRouteProviderInterfa
    *
    * @var array
    */
-  protected $serialized_routes = array();
+  protected $serializedRoutes = [];
 
   /**
    * The current path.
@@ -146,11 +146,12 @@ public function preLoadRoutes($names) {
       throw new \InvalidArgumentException('You must specify the route names to load');
     }
 
-    $routes_to_load = array_diff($names, array_keys($this->serialized_routes));
+    $routes_to_load = array_diff($names, array_keys($this->routes));
+    $routes_to_load = array_diff($routes_to_load, array_keys($this->serializedRoutes));
     if ($routes_to_load) {
       $result = $this->connection->query('SELECT name, route FROM {' . $this->connection->escapeTable($this->tableName) . '} WHERE name IN ( :names[] )', array(':names[]' => $routes_to_load));
       $routes = $result->fetchAllKeyed();
-      $this->serialized_routes += $routes;
+      $this->serializedRoutes += $routes;
     }
   }
 
@@ -162,12 +163,14 @@ public function getRoutesByNames($names) {
 
     foreach ($names as $name) {
       // The specified route name might not exist or might be serialized.
-      if (!isset($this->routes[$name]) && isset($this->serialized_routes[$name])) {
-        $this->routes[$name] = unserialize($this->serialized_routes[$name]);
+      if (!isset($this->routes[$name]) && isset($this->serializedRoutes[$name])) {
+        $this->routes[$name] = unserialize($this->serializedRoutes[$name]);
         // Leave the variable set but free up the memory.
-        $this->serialized_routes[$name] = '';
+        $this->serializedRoutes[$name] = '';
       }
     }
+
+    return array_intersect_key($this->routes, array_flip($names));
   }
 
   /**
@@ -296,7 +299,7 @@ public function getAllRoutes() {
    */
   public function reset() {
     $this->routes  = array();
-    $this->serialized_routes = array();
+    $this->serializedRoutes = array();
   }
 
   /**