diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index e94983b..7e0001c 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -946,6 +946,11 @@ protected function setUp() {
     $this->resetAll();
     $this->kernel->prepareLegacyRequest($request);
 
+    // Explicitly call register() again on the container registered in \Drupal.
+    // @todo This should already be called through
+    //   DrupalKernel::prepareLegacyRequest() -> DrupalKernel::boot() but that
+    //   appears to be calling a different container.
+    \Drupal::service('stream_wrapper_manager')->register();
     // Temporary fix so that when running from run-tests.sh we don't get an
     // empty current path which would indicate we're on the home page.
     $path = current_path();