diff --git a/core/lib/Drupal/Core/Routing/RequestContext.php b/core/lib/Drupal/Core/Routing/RequestContext.php
index 9896cde..c5222c4 100644
--- a/core/lib/Drupal/Core/Routing/RequestContext.php
+++ b/core/lib/Drupal/Core/Routing/RequestContext.php
@@ -55,7 +55,7 @@ public function fromRequest(Request $request) {
       $this->setCompleteBaseUrl($GLOBALS['base_url']);
     }
     if (isset($GLOBALS['base_path'])) {
-      $this->setMainBaseUrl($GLOBALS['base_path']);
+      $this->setMainBaseUrl('/' . ltrim($GLOBALS['base_path']));
     }
   }