diff --git a/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php b/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php
index c54e3f6..8b2e463 100644
--- a/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ExtensionStreamBase.php
@@ -81,6 +81,9 @@ public function dirname($uri = NULL) {
     if (!isset($uri)) {
       $uri = $this->uri;
     }
+    else {
+      $this->uri = $uri;
+    }
 
     list($scheme) = explode('://', $uri, 2);
     $dirname = dirname($this->getTarget($uri));
diff --git a/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php b/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php
index f31d581..7ba9e4c 100644
--- a/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php
+++ b/core/modules/system/tests/src/Kernel/File/ExtensionStreamTest.php
@@ -32,6 +32,13 @@ class ExtensionStreamTest extends KernelTestBase {
   protected $baseUrl;
 
   /**
+   * The list of modules to enable.
+   *
+   * @var string[]
+   */
+  public static $modules = ['system'];
+
+  /**
    * {@inheritdoc}
    */
   public function setUp() {
@@ -147,6 +154,13 @@ public function testStreamWrapperMethods($uri, $dirname, $realpath, $getExternal
   }
 
   /**
+   * Test when dirname() is called directly without setting a URI first.
+   */
+  public function testDirnameAsParameter() {
+    $this->assertEquals('module://system', $this->streamWrappers['module']->dirname('module://system/system.admin.css'));
+  }
+
+  /**
    * Provides test cases for testStreamWrapperMethods().
    *
    * @return array[]