diff --git a/composer.json b/composer.json
index 51d4abad825..806a9a98d98 100644
--- a/composer.json
+++ b/composer.json
@@ -42,8 +42,7 @@
             "src/Core/functions.php",
             "src/Collection/functions.php",
             "src/I18n/functions.php",
-            "src/Utility/bootstrap.php",
-            "src/TestSuite/phpunit-forward-compat.php"
+            "src/Utility/bootstrap.php"
         ]
     },
     "autoload-dev": {
diff --git a/src/TestSuite/Constraint/EventFired.php b/src/TestSuite/Constraint/EventFired.php
index 0223458ba3e..917ca191fca 100644
--- a/src/TestSuite/Constraint/EventFired.php
+++ b/src/TestSuite/Constraint/EventFired.php
@@ -1,6 +1,13 @@
 <?php
 namespace Cake\TestSuite\Constraint;
 
+if (class_exists('PHPUnit_Runner_Version') && !class_exists('PHPUnit\Framework\Constraint\Constraint')) {
+    class_alias('PHPUnit_Framework_Constraint', 'PHPUnit\Framework\Constraint\Constraint');
+}
+if (class_exists('PHPUnit_Runner_Version') && !class_exists('PHPUnit\Framework\AssertionFailedError')) {
+    class_alias('PHPUnit_Framework_AssertionFailedError', 'PHPUnit\Framework\AssertionFailedError');
+}
+
 use Cake\Event\EventManager;
 use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\Constraint\Constraint;
diff --git a/src/TestSuite/Constraint/EventFiredWith.php b/src/TestSuite/Constraint/EventFiredWith.php
index 572907a803a..5788ea882e7 100644
--- a/src/TestSuite/Constraint/EventFiredWith.php
+++ b/src/TestSuite/Constraint/EventFiredWith.php
@@ -1,6 +1,13 @@
 <?php
 namespace Cake\TestSuite\Constraint;
 
+if (class_exists('PHPUnit_Runner_Version') && !class_exists('PHPUnit\Framework\Constraint\Constraint')) {
+    class_alias('PHPUnit_Framework_Constraint', 'PHPUnit\Framework\Constraint\Constraint');
+}
+if (class_exists('PHPUnit_Runner_Version') && !class_exists('PHPUnit\Framework\AssertionFailedError')) {
+    class_alias('PHPUnit_Framework_AssertionFailedError', 'PHPUnit\Framework\AssertionFailedError');
+}
+
 use Cake\Event\Event;
 use Cake\Event\EventManager;
 use PHPUnit\Framework\AssertionFailedError;
diff --git a/src/TestSuite/Fixture/FixtureInjector.php b/src/TestSuite/Fixture/FixtureInjector.php
index e902edc5e4c..8be48c4453e 100644
--- a/src/TestSuite/Fixture/FixtureInjector.php
+++ b/src/TestSuite/Fixture/FixtureInjector.php
@@ -14,6 +14,15 @@
  */
 namespace Cake\TestSuite\Fixture;
 
+if (class_exists('PHPUnit_Runner_Version')) {
+    class_alias('PHPUnit_Framework_Test', 'PHPUnit\Framework\Test');
+    if (!class_exists('PHPUnit\Framework\TestSuite')) {
+        class_alias('PHPUnit_Framework_TestSuite', 'PHPUnit\Framework\TestSuite');
+    }
+    class_alias('PHPUnit_Framework_Error_Warning', 'PHPUnit\Framework\Error\Warning');
+    class_alias('PHPUnit_Framework_AssertionFailedError', 'PHPUnit\Framework\AssertionFailedError');
+}
+
 use Cake\TestSuite\TestCase;
 use Exception;
 use PHPUnit\Framework\AssertionFailedError;
diff --git a/src/TestSuite/IntegrationTestCase.php b/src/TestSuite/IntegrationTestCase.php
index 96a2a2ffaa5..ee172928401 100644
--- a/src/TestSuite/IntegrationTestCase.php
+++ b/src/TestSuite/IntegrationTestCase.php
@@ -13,6 +13,10 @@
  */
 namespace Cake\TestSuite;
 
+if (class_exists('PHPUnit_Runner_Version') && !interface_exists('PHPUnit\Exception')) {
+    class_alias('PHPUnit_Exception', 'PHPUnit\Exception');
+}
+
 use Cake\Core\Configure;
 use Cake\Database\Exception as DatabaseException;
 use Cake\Network\Session;
diff --git a/src/TestSuite/TestSuite.php b/src/TestSuite/TestSuite.php
index 0f12a615057..9deb87ca5b5 100644
--- a/src/TestSuite/TestSuite.php
+++ b/src/TestSuite/TestSuite.php
@@ -16,6 +16,10 @@
  */
 namespace Cake\TestSuite;
 
+if (class_exists('PHPUnit_Runner_Version') && !class_exists('PHPUnit\Framework\TestSuite')) {
+    class_alias('PHPUnit_Framework_TestSuite', 'PHPUnit\Framework\TestSuite');
+}
+
 use Cake\Filesystem\Folder;
 use PHPUnit\Framework\TestSuite as BaseTestSuite;
 
diff --git a/src/TestSuite/phpunit-forward-compat.php b/src/TestSuite/phpunit-forward-compat.php
deleted file mode 100644
index 595d3d4b783..00000000000
--- a/src/TestSuite/phpunit-forward-compat.php
+++ /dev/null
@@ -1,10 +0,0 @@
-<?php
-
-if (class_exists('PHPUnit_Runner_Version')) {
-    class_alias('PHPUnit_Framework_Test', 'PHPUnit\Framework\Test');
-    class_alias('PHPUnit_Framework_TestSuite', 'PHPUnit\Framework\TestSuite');
-    class_alias('PHPUnit_Exception', 'PHPUnit\Exception');
-    class_alias('PHPUnit_Framework_Error_Warning', 'PHPUnit\Framework\Error\Warning');
-    class_alias('PHPUnit_Framework_Constraint', 'PHPUnit\Framework\Constraint\Constraint');
-    class_alias('PHPUnit_Framework_AssertionFailedError', 'PHPUnit\Framework\AssertionFailedError');
-}