diff --git a/tests/phpunit/includes/phpunit6-compat.php b/tests/phpunit/includes/phpunit6-compat.php
index a5b0a9f5a8..64089102dc 100644
--- a/tests/phpunit/includes/phpunit6-compat.php
+++ b/tests/phpunit/includes/phpunit6-compat.php
@@ -6,6 +6,7 @@ if ( class_exists( 'PHPUnit\Runner\Version' ) && version_compare( PHPUnit\Runner
 	class_alias( 'PHPUnit\Framework\Exception',                  'PHPUnit_Framework_Exception' );
 	class_alias( 'PHPUnit\Framework\ExpectationFailedException', 'PHPUnit_Framework_ExpectationFailedException' );
 	class_alias( 'PHPUnit\Framework\Error\Notice',               'PHPUnit_Framework_Error_Notice' );
+	class_alias( 'PHPUnit\Framework\Error\Warning',              'PHPUnit_Framework_Error_Warning' );
 	class_alias( 'PHPUnit\Framework\Test',                       'PHPUnit_Framework_Test' );
 	class_alias( 'PHPUnit\Framework\Warning',                    'PHPUnit_Framework_Warning' );
 	class_alias( 'PHPUnit\Framework\AssertionFailedError',       'PHPUnit_Framework_AssertionFailedError' );