diff -u b/core/modules/system/lib/Drupal/system/Tests/System/ShutdownFunctionsTest.php b/core/modules/system/lib/Drupal/system/Tests/System/ShutdownFunctionsTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/System/ShutdownFunctionsTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/ShutdownFunctionsTest.php
@@ -36,13 +36,19 @@
     $arg1 = $this->randomName();
     $arg2 = $this->randomName();
     $this->drupalGet('system-test/shutdown-functions/' . $arg1 . '/' . $arg2);
-    $this->assertEqual(\Drupal::state()->get('_system_test_first_shutdown_function'), array($arg1, $arg2));
-    $this->assertEqual(\Drupal::state()->get('_system_test_second_shutdown_function'), array($arg1, $arg2));
 
     // If using PHP-FPM then fastcgi_finish_request() will have been fired
-    // preventing further output to the browser.
+    // returning the response before shutdown functions have fired.
     // @see \Drupal\system_test\Controller\SystemTestController::shutdownFunctions()
-    if (strpos($this->drupalGetContent(), 'The function fastcgi_finish_request exists when serving the request.') === FALSE) {
+    $server_using_fastcgi = strpos($this->drupalGetContent(), 'The function fastcgi_finish_request exists when serving the request.');
+    if ($server_using_fastcgi) {
+      // We need to wait to ensure that the shutdown functions have fired.
+      sleep(1);
+    }
+    $this->assertEqual(\Drupal::state()->get('_system_test_first_shutdown_function'), array($arg1, $arg2));
+    $this->assertEqual(\Drupal::state()->get('_system_test_second_shutdown_function'), array($arg1, $arg2));
+
+    if (!$server_using_fastcgi) {
       // Make sure exceptions displayed through
       // \Drupal\Core\Utility\Error::renderExceptionSafe() are correctly
       // escaped.