diff --git a/core/lib/Drupal/Core/Theme/ThemeNegotiator.php b/core/lib/Drupal/Core/Theme/ThemeNegotiator.php
index 089bc06..97b8f65 100644
--- a/core/lib/Drupal/Core/Theme/ThemeNegotiator.php
+++ b/core/lib/Drupal/Core/Theme/ThemeNegotiator.php
@@ -67,14 +67,15 @@ public function applies($route_name = '', Route $route = NULL) {
    */
   public function determineActiveTheme(RouteMatchInterface $route_match) {
     $route = $route_match->getRouteObject() ?: NULL;
-
-    // If no route was found (for example on a 404 page), we still need to
-    // evaluate all available theme negotiators.
-    $negotiator_service_ids = ($route && $route->getOption('_theme_negotiators')) ? $route->getOption('_theme_negotiators') : $this->negotiator_service_ids;
+    $route_theme_negotiator_ids = ($route && $route->getOption('_theme_negotiators')) ? $route->getOption('_theme_negotiators') : array();
+    $negotiator_service_ids = $route_theme_negotiator_ids ?: $this->negotiator_service_ids;
 
     foreach ($negotiator_service_ids as $service_id) {
       $negotiator = $this->container->get($service_id);
-      if (!empty($route) || $negotiator->applies($route_match->getRouteName(), $route)) {
+      // If no route was found (for example on a 404 page) or no theme
+      // negotiators were stored on the route, we need to evaluate all available
+      // theme negotiators.
+      if ($route_theme_negotiator_ids || $negotiator->applies($route_match->getRouteName(), $route)) {
         $theme = $negotiator->determineActiveTheme($route_match);
         if ($theme !== NULL && $this->themeAccess->checkAccess($theme)) {
           return $theme;