diff --git a/core/tests/Drupal/TestSuites/FunctionalJavascriptTestSuite.php b/core/tests/Drupal/TestSuites/FunctionalJavascriptTestSuite.php
index 66b0bd9..17294ce 100644
--- a/core/tests/Drupal/TestSuites/FunctionalJavascriptTestSuite.php
+++ b/core/tests/Drupal/TestSuites/FunctionalJavascriptTestSuite.php
@@ -2,6 +2,10 @@
 
 namespace Drupal\TestSuites;
 
+// Require the base class. We do this to avoid making the test suite classes
+// autoloadable.
+require_once __DIR__ . '/TestSuiteBase.php';
+
 /**
  * Discovers tests for the functional-javascript test suite.
  */
diff --git a/core/tests/Drupal/TestSuites/FunctionalTestSuite.php b/core/tests/Drupal/TestSuites/FunctionalTestSuite.php
index 06f9e4d..233b3db 100644
--- a/core/tests/Drupal/TestSuites/FunctionalTestSuite.php
+++ b/core/tests/Drupal/TestSuites/FunctionalTestSuite.php
@@ -2,6 +2,10 @@
 
 namespace Drupal\TestSuites;
 
+// Require the base class. We do this to avoid making the test suite classes
+// autoloadable.
+require_once __DIR__ . '/TestSuiteBase.php';
+
 /**
  * Discovers tests for the functional test suite.
  */
diff --git a/core/tests/Drupal/TestSuites/KernelTestSuite.php b/core/tests/Drupal/TestSuites/KernelTestSuite.php
index 9c9e830..dbfe8b8 100644
--- a/core/tests/Drupal/TestSuites/KernelTestSuite.php
+++ b/core/tests/Drupal/TestSuites/KernelTestSuite.php
@@ -2,6 +2,10 @@
 
 namespace Drupal\TestSuites;
 
+// Require the base class. We do this to avoid making the test suite classes
+// autoloadable.
+require_once __DIR__ . '/TestSuiteBase.php';
+
 /**
  * Discovers tests for the kernel test suite.
  */
diff --git a/core/tests/Drupal/TestSuites/UnitTestSuite.php b/core/tests/Drupal/TestSuites/UnitTestSuite.php
index 3bc19c0..3c30cdd 100644
--- a/core/tests/Drupal/TestSuites/UnitTestSuite.php
+++ b/core/tests/Drupal/TestSuites/UnitTestSuite.php
@@ -2,6 +2,10 @@
 
 namespace Drupal\TestSuites;
 
+// Require the base class. We do this to avoid making the test suite classes
+// autoloadable.
+require_once __DIR__ . '/TestSuiteBase.php';
+
 /**
  * Discovers tests for the unit test suite.
  */
diff --git a/core/tests/Drupal/Tests/TestSuites/TestSuiteBaseTest.php b/core/tests/Drupal/Tests/TestSuites/TestSuiteBaseTest.php
index 4cd7dd7..6a43ea4 100644
--- a/core/tests/Drupal/Tests/TestSuites/TestSuiteBaseTest.php
+++ b/core/tests/Drupal/Tests/TestSuites/TestSuiteBaseTest.php
@@ -5,6 +5,10 @@
 use Drupal\TestSuites\TestSuiteBase;
 use org\bovigo\vfs\vfsStream;
 
+// Require the base class. We do this to avoid making the test suite classes
+// autoloadable.
+require_once __DIR__ . '/../../TestSuites/TestSuiteBase.php';
+
 /**
  * @coversDefaultClass \Drupal\TestSuites\TestSuiteBase
  *