diff --git a/src/wp-includes/rest-api.php b/src/wp-includes/rest-api.php
index 3b158ea07f..06bb9f9f80 100644
--- a/src/wp-includes/rest-api.php
+++ b/src/wp-includes/rest-api.php
@@ -19,8 +19,6 @@ define( 'REST_API_VERSION', '2.0' );
  *
  * @since 4.4.0
  *
- * @global WP_REST_Server $wp_rest_server ResponseHandler instance (usually WP_REST_Server).
- *
  * @param string $namespace The first URL segment after core prefix. Should be unique to your package/plugin.
  * @param string $route     The base URL for route you are adding.
  * @param array  $args      Optional. Either an array of options for the endpoint, or an array of arrays for
@@ -30,9 +28,6 @@ define( 'REST_API_VERSION', '2.0' );
  * @return bool True on success, false on error.
  */
 function register_rest_route( $namespace, $route, $args = array(), $override = false ) {
-	/** @var WP_REST_Server $wp_rest_server */
-	global $wp_rest_server;
-
 	if ( empty( $namespace ) ) {
 		/*
 		 * Non-namespaced routes are not allowed, with the exception of the main
@@ -74,7 +69,7 @@ function register_rest_route( $namespace, $route, $args = array(), $override = f
 	}
 
 	$full_route = '/' . trim( $namespace, '/' ) . '/' . trim( $route, '/' );
-	$wp_rest_server->register_route( $namespace, $full_route, $args, $override );
+	rest_get_server()->register_route( $namespace, $full_route, $args, $override );
 	return true;
 }
 
@@ -245,7 +240,6 @@ function create_initial_rest_routes() {
  * @since 4.4.0
  *
  * @global WP             $wp             Current WordPress environment instance.
- * @global WP_REST_Server $wp_rest_server ResponseHandler instance (usually WP_REST_Server).
  */
 function rest_api_loaded() {
 	if ( empty( $GLOBALS['wp']->query_vars['rest_route'] ) ) {
@@ -387,8 +381,6 @@ function rest_url( $path = '', $scheme = 'json' ) {
  *
  * @since 4.4.0
  *
- * @global WP_REST_Server $wp_rest_server ResponseHandler instance (usually WP_REST_Server).
- *
  * @param WP_REST_Request|string $request Request.
  * @return WP_REST_Response REST response.
  */
@@ -704,7 +696,6 @@ function rest_output_link_header() {
  * @since 4.4.0
  *
  * @global mixed          $wp_rest_auth_cookie
- * @global WP_REST_Server $wp_rest_server      REST server instance.
  *
  * @param WP_Error|mixed $result Error from another authentication handler,
  *                               null if we should handle it, or another value
@@ -716,7 +707,7 @@ function rest_cookie_check_errors( $result ) {
 		return $result;
 	}
 
-	global $wp_rest_auth_cookie, $wp_rest_server;
+	global $wp_rest_auth_cookie;
 
 	/*
 	 * Is cookie authentication being used? (If we get an auth
@@ -750,7 +741,7 @@ function rest_cookie_check_errors( $result ) {
 	}
 
 	// Send a refreshed nonce in header.
-	$wp_rest_server->send_header( 'X-WP-Nonce', wp_create_nonce( 'wp_rest' ) );
+	rest_get_server()->send_header( 'X-WP-Nonce', wp_create_nonce( 'wp_rest' ) );
 
 	return true;
 }
diff --git a/tests/phpunit/tests/rest-api.php b/tests/phpunit/tests/rest-api.php
index 689cbdfbae..90a480d641 100644
--- a/tests/phpunit/tests/rest-api.php
+++ b/tests/phpunit/tests/rest-api.php
@@ -16,7 +16,12 @@ class Tests_REST_API extends WP_UnitTestCase {
 	public function setUp() {
 		// Override the normal server with our spying server.
 		$GLOBALS['wp_rest_server'] = new Spy_REST_Server();
-		parent::setup();
+		parent::setUp();
+	}
+
+	public function tearDown() {
+		remove_filter( 'wp_rest_server_class', array( $this, 'filter_wp_rest_server_class' ) );
+		parent::tearDown();
 	}
 
 	/**
@@ -446,4 +451,21 @@ class Tests_REST_API extends WP_UnitTestCase {
 	public function test_rest_parse_date_force_utc( $string, $value ) {
 		$this->assertEquals( $value, rest_parse_date( $string, true ) );
 	}
+
+	public function filter_wp_rest_server_class( $class_name ) {
+		return 'Spy_REST_Server';
+	}
+
+	public function test_register_rest_route_without_server() {
+		$GLOBALS['wp_rest_server'] = null;
+		add_filter( 'wp_rest_server_class', array( $this, 'filter_wp_rest_server_class' ) );
+
+		register_rest_route( 'test-ns', '/test', array(
+			'methods'  => array( 'GET' ),
+			'callback' => '__return_null',
+		) );
+
+		$routes = $GLOBALS['wp_rest_server']->get_routes();
+		$this->assertEquals( $routes['/test-ns/test'][0]['methods'], array( 'GET' => true ) );
+	}
 }