diff --git a/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php b/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php
index 45214ee..4def427 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/ConfigMapperInterface.php
@@ -52,6 +52,8 @@ public function getBaseRoute();
    *
    * @param \Symfony\Component\Routing\Route $route
    *   The route object used as base route.
+   *
+   * @see \Drupal\config_translation\Routing\RouteSubscriber::alterRoutes()
    */
   public function setBaseRoute(Route $route);
 
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php b/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php
index 3f6a208..1351e72 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/ConfigNamesMapper.php
@@ -144,6 +144,9 @@ public function getBaseRouteParameters() {
    * {@inheritdoc}
    */
   public function getBaseRoute() {
+    // The base route cannot be set directly in the constructor because during
+    // route rebuilding we need to instantiate the mappers before the respective
+    // routes are available.
     if (!isset($this->baseRoute)) {
       $this->baseRoute = $this->routeProvider->getRouteByName($this->getBaseRouteName());
     }
diff --git a/core/modules/config_translation/lib/Drupal/config_translation/Routing/RouteSubscriber.php b/core/modules/config_translation/lib/Drupal/config_translation/Routing/RouteSubscriber.php
index 2614dc8..6f24a68 100644
--- a/core/modules/config_translation/lib/Drupal/config_translation/Routing/RouteSubscriber.php
+++ b/core/modules/config_translation/lib/Drupal/config_translation/Routing/RouteSubscriber.php
@@ -18,11 +18,18 @@
 class RouteSubscriber extends RouteSubscriberBase {
 
   /**
-   * The mapper plugin discovery service.
+   * An array of all configuration mappers, keyed by ID.
    *
-   * @var \Drupal\config_translation\ConfigMapperManagerInterface
+   * @var \Drupal\config_translation\ConfigMapperInterface[]
    */
-  protected $mapperManager;
+  protected $mappers;
+
+  /**
+   * A mapping of configuration mappers to their base route name.
+   *
+   * @var array
+   */
+  protected $baseRouteNames = array();
 
   /**
    * Constructs a new RouteSubscriber.
@@ -31,13 +38,14 @@ class RouteSubscriber extends RouteSubscriberBase {
    *   The mapper plugin discovery service.
    */
   public function __construct(ConfigMapperManagerInterface $mapper_manager) {
-    $this->mapperManager = $mapper_manager;
+    $this->mappers = $mapper_manager->getMappers();
 
-    $this->mappers = $this->mapperManager->getMappers();
-    $this->neededMapperBaseRoutes = array();
-    $this->baseRoutesMapping = array();
-    foreach ($this->mappers as $id => $mapper) {
-      $this->neededMapperBaseRoutes[$id] = $mapper->getBaseRouteName();
+    // The entire list of base route names is needed so we can check each route
+    // collection for matching routes in RouteSubscriber::alterRoutes(). In
+    // order to pass the route information to the configuration mapper we then
+    // need the respective mapper ID for the base route name.
+    foreach ($this->mappers as $mapper_id => $mapper) {
+      $this->baseRouteNames[$mapper_id] = $mapper->getBaseRouteName();
     }
   }
 
@@ -45,21 +53,22 @@ public function __construct(ConfigMapperManagerInterface $mapper_manager) {
    * {@inheritdoc}
    */
   protected function alterRoutes(RouteCollection $collection, $provider) {
-    foreach ($this->neededMapperBaseRoutes as $mapper_id => $route_name) {
+    foreach ($this->baseRouteNames as $mapper_id => $route_name) {
       if ($route = $collection->get($route_name)) {
-        $this->baseRoutesMapping[$mapper_id] = $route;
-      }
-    }
+        $mapper = $this->mappers[$mapper_id];
+        $mapper->setBaseRoute($route);
+        $collection->add($mapper->getOverviewRouteName(), $mapper->getOverviewRoute());
+        $collection->add($mapper->getAddRouteName(), $mapper->getAddRoute());
+        $collection->add($mapper->getEditRouteName(), $mapper->getEditRoute());
+        $collection->add($mapper->getDeleteRouteName(), $mapper->getDeleteRoute());
 
-    foreach ($this->mappers as $id => $mapper) {
-      if (!isset($this->baseRoutesMapping[$id])) {
-        throw new \Exception('No freaking idea: ');
+        // We do not need to check for the same base route name on the next
+        // invocation.
+        unset($this->baseRouteNames[$mapper_id]);
       }
-      $mapper->setBaseRoute($this->baseRoutesMapping[$id]);
-      $collection->add($mapper->getOverviewRouteName(), $mapper->getOverviewRoute());
-      $collection->add($mapper->getAddRouteName(), $mapper->getAddRoute());
-      $collection->add($mapper->getEditRouteName(), $mapper->getEditRoute());
-      $collection->add($mapper->getDeleteRouteName(), $mapper->getDeleteRoute());
+    }
+    if (!empty($this->baseRouteNames)) {
+      throw new \Exception('Well, if @dawehner has NFI, what is @tstoeckler supposed to say?!');
     }
   }
 
@@ -68,8 +77,9 @@ protected function alterRoutes(RouteCollection $collection, $provider) {
    */
   public static function getSubscribedEvents() {
     $events = parent::getSubscribedEvents();
+    // This route subscriber adds routes based on the existence of other routes,
+    // so all route subscribers that add routes need to run before this one.
     $events[RoutingEvents::ALTER] = array('onAlterRoutes', -10);
-
     return $events;
   }