diff --git a/tests/phpunit/includes/abstract-testcase.php b/tests/phpunit/includes/abstract-testcase.php
index 8b1163a531..6cc2f5f022 100644
--- a/tests/phpunit/includes/abstract-testcase.php
+++ b/tests/phpunit/includes/abstract-testcase.php
@@ -12,7 +12,7 @@ require_once __DIR__ . '/trac.php';
  *
  * All WordPress unit tests should inherit from this class.
  */
-abstract class WP_UnitTestCase_Base extends PHPUnit_Framework_TestCase {
+abstract class WP_UnitTestCase_Base extends PHPUnit\Framework\TestCase {
 
 	protected static $forced_tickets   = array();
 	protected $expected_deprecated     = array();
diff --git a/tests/phpunit/includes/bootstrap.php b/tests/phpunit/includes/bootstrap.php
index dcde8fd2ea..d628d62c09 100644
--- a/tests/phpunit/includes/bootstrap.php
+++ b/tests/phpunit/includes/bootstrap.php
@@ -37,9 +37,9 @@ if ( ! is_readable( $config_file_path ) ) {
 require_once $config_file_path;
 require_once __DIR__ . '/functions.php';
 
-if ( version_compare( tests_get_phpunit_version(), '8.0', '>=' ) ) {
+if ( version_compare( tests_get_phpunit_version(), '5.4', '<' ) || version_compare( tests_get_phpunit_version(), '8.0', '>=' ) ) {
 	printf(
-		"Error: Looks like you're using PHPUnit %s. WordPress is currently only compatible with PHPUnit up to 7.x.\n",
+		"Error: Looks like you're using PHPUnit %s. WordPress requires at least PHPUnit 5.4 and is currently only compatible with PHPUnit up to 7.x.\n",
 		tests_get_phpunit_version()
 	);
 	echo "Please use the latest PHPUnit version from the 7.x branch.\n";
diff --git a/tests/phpunit/includes/functions.php b/tests/phpunit/includes/functions.php
index e20114386a..dd80e887ce 100644
--- a/tests/phpunit/includes/functions.php
+++ b/tests/phpunit/includes/functions.php
@@ -10,8 +10,7 @@ function tests_get_phpunit_version() {
 	if ( class_exists( 'PHPUnit_Runner_Version' ) ) {
 		$version = PHPUnit_Runner_Version::id();
 	} elseif ( class_exists( 'PHPUnit\Runner\Version' ) ) {
-		// Must be parsable by PHP 5.2.x.
-		$version = call_user_func( 'PHPUnit\Runner\Version::id' );
+		$version = PHPUnit\Runner\Version::id();
 	} else {
 		$version = 0;
 	}