diff --git a/core/lib/Drupal/Core/StreamWrapper/PublicStream.php b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
index e2b78ec..e05bd82 100644
--- a/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/PublicStream.php
@@ -51,7 +51,7 @@ public function getDirectoryPath() {
    */
   public function getExternalUrl() {
     $path = str_replace('\\', '/', $this->getTarget());
-    return $GLOBALS['base_url'] . '/' . self::getDirectoryPath() . '/' . UrlHelper::encodePath($path);
+    return $GLOBALS['base_url'] . '/' . $this->getDirectoryPath() . '/' . UrlHelper::encodePath($path);
   }
 
   /**