diff --git a/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php
index 6e4f82d..c6fbdd0 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ExceptionTestSiteSubscriber.php
@@ -79,7 +79,6 @@ public function onResponse(FilterResponseEvent $event) {
       $response->headers->add([
         'X-Drupal-Memory-Peak' => round($memory_usage / 1024 / 1024, 2),
       ]);
-      $event->setResponse($response);
     }
   }
 
diff --git a/core/modules/simpletest/src/Tests/BrokenSetUpTest.php b/core/modules/simpletest/src/Tests/BrokenSetUpTest.php
index dae351b..4067f79 100644
--- a/core/modules/simpletest/src/Tests/BrokenSetUpTest.php
+++ b/core/modules/simpletest/src/Tests/BrokenSetUpTest.php
@@ -32,7 +32,7 @@ class BrokenSetUpTest extends WebTestBase {
   /**
    * The memory limit for this test, Testing module requires 128M.
    */
-  protected $memoryUsageTrigger = 128;
+  protected $memoryUsageTrigger = 140;
 
   /**
    * The path to the shared trigger file.
diff --git a/core/modules/simpletest/src/Tests/InstallationProfileModuleTestsTest.php b/core/modules/simpletest/src/Tests/InstallationProfileModuleTestsTest.php
index 4cca66a..a58d378 100644
--- a/core/modules/simpletest/src/Tests/InstallationProfileModuleTestsTest.php
+++ b/core/modules/simpletest/src/Tests/InstallationProfileModuleTestsTest.php
@@ -33,7 +33,7 @@ class InstallationProfileModuleTestsTest extends WebTestBase {
   /**
    * The memory limit for this test, Testing module requires 128M.
    */
-  protected $memoryUsageTrigger = 128;
+  protected $memoryUsageTrigger = 140;
 
   /**
    * Use the Testing profile.
diff --git a/core/modules/simpletest/src/Tests/MissingCheckedRequirementsTest.php b/core/modules/simpletest/src/Tests/MissingCheckedRequirementsTest.php
index 667181e..5f95148 100644
--- a/core/modules/simpletest/src/Tests/MissingCheckedRequirementsTest.php
+++ b/core/modules/simpletest/src/Tests/MissingCheckedRequirementsTest.php
@@ -26,7 +26,7 @@ class MissingCheckedRequirementsTest extends WebTestBase {
   /**
    * The memory limit for this test, Testing module requires 128M.
    */
-  protected $memoryUsageTrigger = 128;
+  protected $memoryUsageTrigger = 140;
 
   protected function setUp() {
     parent::setUp();
diff --git a/core/modules/simpletest/src/Tests/OtherInstallationProfileTestsTest.php b/core/modules/simpletest/src/Tests/OtherInstallationProfileTestsTest.php
index 74ce9f2..d7be9ab 100644
--- a/core/modules/simpletest/src/Tests/OtherInstallationProfileTestsTest.php
+++ b/core/modules/simpletest/src/Tests/OtherInstallationProfileTestsTest.php
@@ -41,7 +41,7 @@ class OtherInstallationProfileTestsTest extends WebTestBase {
   /**
    * The memory limit for this test, Testing module requires 128M.
    */
-  protected $memoryUsageTrigger = 128;
+  protected $memoryUsageTrigger = 140;
 
   /**
    * An administrative user with permission to administer unit tests.
diff --git a/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php b/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
index cfd7bc4..94aefa2 100644
--- a/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
+++ b/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
@@ -27,7 +27,7 @@ class SimpleTestBrowserTest extends WebTestBase {
   /**
    * The memory limit for this test, Testing module requires 128M.
    */
-  protected $memoryUsageTrigger = 128;
+  protected $memoryUsageTrigger = 140;
 
   public function setUp() {
     parent::setUp();
diff --git a/core/modules/simpletest/src/Tests/SimpleTestTest.php b/core/modules/simpletest/src/Tests/SimpleTestTest.php
index fc4e865..85b8187 100644
--- a/core/modules/simpletest/src/Tests/SimpleTestTest.php
+++ b/core/modules/simpletest/src/Tests/SimpleTestTest.php
@@ -29,7 +29,7 @@ class SimpleTestTest extends WebTestBase {
   /**
    * The memory limit for this test, Testing module requires 128M.
    */
-  protected $memoryUsageTrigger = 128;
+  protected $memoryUsageTrigger = 140;
 
   /**
    * The results array that has been parsed by getTestResults().
@@ -217,6 +217,13 @@ function stubTest() {
 
     // This causes the debug message asserted in confirmStubResults().
     debug('Foo', 'Debug', FALSE);
+
+    // This causes \Drupal\simpletest\WebTestBase::curlHeaderCallback() to fail.
+    // Set an absurdly low limit and get a page.
+    $old_limit = $this->memoryUsageTrigger;
+    $this->memoryUsageTrigger = 1;
+    $this->drupalGet($user->url());
+    $this->memoryUsageTrigger = $old_limit;
   }
 
   /**
@@ -255,7 +262,9 @@ function confirmStubTestResults() {
 
     $this->assertAssertion("Debug: 'Foo'", 'Debug', 'Fail', 'SimpleTestTest.php', 'Drupal\simpletest\Tests\SimpleTestTest->stubTest()');
 
-    $this->assertEqual('15 passes, 3 fails, 2 exceptions, 3 debug messages', $this->childTestResults['summary']);
+    $this->assertAssertion("exceeded acceptable maximum (1MB)", 'Other', 'Fail', 'WebTestBase.php', 'Drupal\simpletest\WebTestBase->curlExec()');
+
+    $this->assertEqual('17 passes, 4 fails, 2 exceptions, 4 debug messages', $this->childTestResults['summary']);
 
     $this->testIds[] = $test_id = $this->getTestIdFromResults();
     $this->assertTrue($test_id, 'Found test ID in results.');