diff --git a/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php
index 96bd6d8..0422bf0 100644
--- a/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/CustomPageExceptionHtmlSubscriber.php
@@ -63,7 +63,7 @@ protected static function getPriority() {
    */
   public function on403(GetResponseForExceptionEvent $event) {
     $path = $this->aliasManager->getPathByAlias($this->configFactory->get('system.site')->get('page.403'));
-    $this->makeSubrequest($event, $event->getRequest()->getBaseUrl() . $path, Response::HTTP_FORBIDDEN);
+    $this->makeSubrequest($event, $event->getRequest()->getBasePath() . '/' . $path, Response::HTTP_FORBIDDEN);
   }
 
   /**
@@ -71,7 +71,7 @@ public function on403(GetResponseForExceptionEvent $event) {
    */
   public function on404(GetResponseForExceptionEvent $event) {
     $path = $this->aliasManager->getPathByAlias($this->configFactory->get('system.site')->get('page.404'));
-    $this->makeSubrequest($event, $event->getRequest()->getBaseUrl() . $path, Response::HTTP_NOT_FOUND);
+    $this->makeSubrequest($event, $event->getRequest()->getBasePath() . '/' . $path, Response::HTTP_NOT_FOUND);
   }
 
 }
diff --git a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
index 06073ea..d6782b2 100644
--- a/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/DefaultExceptionHtmlSubscriber.php
@@ -96,9 +96,9 @@ public function on404(GetResponseForExceptionEvent $event) {
   protected function makeSubrequest(GetResponseForExceptionEvent $event, $url, $status_code) {
     $request = $event->getRequest();
 
-    $current_url = $request->getUri();
+    $current_url = $request->getBasePath() . $request->getPathInfo();
 
-    if ($url && $url != $current_url) {
+    if ($url != $request->getBasePath() . '/' && $url != $current_url) {
       if ($request->getMethod() === 'POST') {
         $sub_request = Request::create($url, 'POST', drupal_get_destination() + ['_exception_statuscode' => $status_code] + $request->request->all(), $request->cookies->all(), [], $request->server->all());
       }