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 6f24a68..077fe1f 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
@@ -67,8 +67,8 @@ protected function alterRoutes(RouteCollection $collection, $provider) {
         unset($this->baseRouteNames[$mapper_id]);
       }
     }
-    if (!empty($this->baseRouteNames)) {
-      throw new \Exception('Well, if @dawehner has NFI, what is @tstoeckler supposed to say?!');
+    if ($provider == 'dynamic_routes' && !empty($this->baseRouteNames)) {
+      throw new \RuntimeException(sprintf('The following routes are needed by configuration mappers but were not found: %s', implode(', ', $this->baseRouteNames)));
     }
   }
 
@@ -79,7 +79,10 @@ 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);
+    // Field UI's route subscriber, for example, has priority -100, but provides
+    // routes for which we need to generate translation routes so this priority
+    // needs to be lower than that.
+    $events[RoutingEvents::ALTER] = array('onAlterRoutes', -1000);
     return $events;
   }