diff --git a/.gitignore b/.gitignore
index 8e37be718b..792c0c8ccb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@ wp-tests-config.php
 .htaccess
 
 # Files and folders related to build/test tools
+.phpunit.result.cache
 /phpunit.xml
 /.phpcs.xml
 /phpcs.xml
diff --git a/composer.json b/composer.json
index 804dfb090c..9da1af9769 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,6 @@
 		"squizlabs/php_codesniffer": "3.6.0",
 		"wp-coding-standards/wpcs": "~2.3.0",
 		"phpcompatibility/phpcompatibility-wp": "~2.1.2",
-		"phpunit/phpunit": "^5.7 || ^6.5 || ^7.5",
 		"yoast/phpunit-polyfills": "^1.0"
 	},
 	"scripts": {
diff --git a/tests/phpunit/includes/bootstrap.php b/tests/phpunit/includes/bootstrap.php
index b557efd3d9..fed800ef3c 100644
--- a/tests/phpunit/includes/bootstrap.php
+++ b/tests/phpunit/includes/bootstrap.php
@@ -37,12 +37,12 @@ if ( defined( 'WP_RUN_CORE_TESTS' ) && WP_RUN_CORE_TESTS && ! is_dir( ABSPATH )
 
 $phpunit_version = tests_get_phpunit_version();
 
-if ( version_compare( $phpunit_version, '5.7', '<' ) || version_compare( $phpunit_version, '8.0', '>=' ) ) {
+if ( version_compare( $phpunit_version, '5.7.21', '<' ) ) {
 	printf(
-		"Error: Looks like you're using PHPUnit %s. WordPress requires at least PHPUnit 5.7 and is currently only compatible with PHPUnit up to 7.x.\n",
+		"Error: Looks like you're using PHPUnit %s. WordPress requires at least PHPUnit 5.7.21.\n",
 		$phpunit_version
 	);
-	echo "Please use the latest PHPUnit version from the 7.x branch.\n";
+	echo "Please use the latest PHPUnit version supported for the PHP version you are running the tests on.\n";
 	exit( 1 );
 }