diff --git a/tests/phpunit/includes/bootstrap.php b/tests/phpunit/includes/bootstrap.php
index b4bff16698..089cc59ef1 100644
--- a/tests/phpunit/includes/bootstrap.php
+++ b/tests/phpunit/includes/bootstrap.php
@@ -16,7 +16,7 @@ $config_file_path .= '/wp-tests-config.php';
  * Globalize some WordPress variables, because PHPUnit loads this file inside a function
  * See: https://github.com/sebastianbergmann/phpunit/issues/325
  */
-global $wpdb, $current_site, $current_blog, $wp_rewrite, $shortcode_tags, $wp, $phpmailer;
+global $wpdb, $current_site, $current_blog, $wp_rewrite, $shortcode_tags, $wp, $phpmailer, $wp_theme_directories;
 
 if ( !is_readable( $config_file_path ) ) {
 	die( "ERROR: wp-tests-config.php is missing! Please use wp-tests-config-sample.php to create a config file.\n" );
@@ -53,8 +53,11 @@ $multisite = $multisite || ( defined( 'MULTISITE' ) && MULTISITE );
 require_once( dirname( __FILE__ ) . '/mock-mailer.php' );
 $phpmailer = new MockPHPMailer();
 
-// Add a symlink to the empty default theme to the themes directory, so it can be used for the tests.
-_symlink_default_theme();
+// Set the theme to our special empty theme, to avoid interference from the current Twenty* theme.
+if ( ! defined( 'WP_DEFAULT_THEME' ) ) {
+	define( 'WP_DEFAULT_THEME', 'default' );
+}
+$wp_theme_directories = array( DIR_TESTDATA . '/themedir1' );
 
 system( WP_PHP_BINARY . ' ' . escapeshellarg( dirname( __FILE__ ) . '/install.php' ) . ' ' . escapeshellarg( $config_file_path ) . ' ' . $multisite );
 
diff --git a/tests/phpunit/includes/functions.php b/tests/phpunit/includes/functions.php
index dc8e472ccd..a8702767ef 100644
--- a/tests/phpunit/includes/functions.php
+++ b/tests/phpunit/includes/functions.php
@@ -161,21 +161,3 @@ function _upload_dir_https( $uploads ) {
 
 	return $uploads;
 }
-
-/**
- * Helper functions to link and unlink the empty default theme into the WordPress install
- */
-function _symlink_default_theme() {
-	_unlink_default_theme();
-	symlink( DIR_TESTDATA . '/themedir1/default', ABSPATH . '/wp-content/themes/default' );
-}
-
-function _unlink_default_theme() {
-	if ( file_exists( ABSPATH . '/wp-content/themes/default' ) ) {
-		unlink( ABSPATH . '/wp-content/themes/default' );
-	}
-}
-// Only unlink when we're in the main process.
-if ( 'phpunit' === substr( $GLOBALS['argv'][0], -7 ) ) {
-	register_shutdown_function( '_unlink_default_theme' );
-}
diff --git a/tests/phpunit/includes/install.php b/tests/phpunit/includes/install.php
index 5db0cc1c5a..50efd43bd7 100644
--- a/tests/phpunit/includes/install.php
+++ b/tests/phpunit/includes/install.php
@@ -9,6 +9,12 @@ error_reporting( E_ALL & ~E_DEPRECATED & ~E_STRICT );
 $config_file_path = $argv[1];
 $multisite = ! empty( $argv[2] );
 
+// Set the theme to our special empty theme, to avoid interference from the current Twenty* theme.
+if ( ! defined( 'WP_DEFAULT_THEME' ) ) {
+	define( 'WP_DEFAULT_THEME', 'default' );
+}
+$wp_theme_directories = array( dirname( __FILE__ ) . '/../data/themedir1' );
+
 define( 'WP_INSTALLING', true );
 require_once $config_file_path;
 require_once dirname( __FILE__ ) . '/functions.php';
diff --git a/tests/phpunit/tests/theme.php b/tests/phpunit/tests/theme.php
index 62a88b998f..4cfba15e45 100644
--- a/tests/phpunit/tests/theme.php
+++ b/tests/phpunit/tests/theme.php
@@ -14,16 +14,27 @@ class Tests_Theme extends WP_UnitTestCase {
 	);
 
 	function setUp() {
+		global $wp_theme_directories;
+
 		parent::setUp();
+
+		$backup_wp_theme_directories = $wp_theme_directories;
+		$wp_theme_directories = array( WP_CONTENT_DIR . '/themes' );
+
 		add_filter( 'extra_theme_headers', array( $this, '_theme_data_extra_headers' ) );
 		wp_clean_themes_cache();
 		unset( $GLOBALS['wp_themes'] );
 	}
 
 	function tearDown() {
+		global $wp_theme_directories;
+
+		$wp_theme_directories = $this->wp_theme_directories;
+
 		remove_filter( 'extra_theme_headers', array( $this, '_theme_data_extra_headers' ) );
 		wp_clean_themes_cache();
 		unset( $GLOBALS['wp_themes'] );
+
 		parent::tearDown();
 	}