diff --git a/src/wp-includes/rest-api.php b/src/wp-includes/rest-api.php
index 0eee75c772..620ca925b9 100644
--- a/src/wp-includes/rest-api.php
+++ b/src/wp-includes/rest-api.php
@@ -91,10 +91,15 @@ function rest_api_init() {
  * @since 4.4.0
  *
  * @see add_rewrite_rule()
+ * @global WP_Rewrite $wp_rewrite
  */
 function rest_api_register_rewrites() {
+	global $wp_rewrite;
+
 	add_rewrite_rule( '^' . rest_get_url_prefix() . '/?$','index.php?rest_route=/','top' );
 	add_rewrite_rule( '^' . rest_get_url_prefix() . '/(.*)?','index.php?rest_route=/$matches[1]','top' );
+	add_rewrite_rule( '^' . $wp_rewrite->index . '/' . rest_get_url_prefix() . '/?$','index.php?rest_route=/','top' );
+	add_rewrite_rule( '^' . $wp_rewrite->index . '/' . rest_get_url_prefix() . '/(.*)?','index.php?rest_route=/$matches[1]','top' );
 }
 
 /**
@@ -176,6 +181,7 @@ function rest_get_url_prefix() {
  * @since 4.4.0
  *
  * @todo Check if this is even necessary
+ * @global WP_Rewrite $wp_rewrite
  *
  * @param int    $blog_id Optional. Blog ID. Default of null returns URL for current blog.
  * @param string $path    Optional. REST route. Default '/'.
@@ -188,7 +194,14 @@ function get_rest_url( $blog_id = null, $path = '/', $scheme = 'rest' ) {
 	}
 
 	if ( is_multisite() && get_blog_option( $blog_id, 'permalink_structure' ) || get_option( 'permalink_structure' ) ) {
-		$url = get_home_url( $blog_id, rest_get_url_prefix(), $scheme );
+		global $wp_rewrite;
+
+		if ( $wp_rewrite->using_index_permalinks() ) {
+			$url = get_home_url( $blog_id, $wp_rewrite->index . '/' . rest_get_url_prefix(), $scheme );
+		} else {
+			$url = get_home_url( $blog_id, rest_get_url_prefix(), $scheme );
+		}
+
 		$url .= '/' . ltrim( $path, '/' );
 	} else {
 		$url = trailingslashit( get_home_url( $blog_id, '', $scheme ) );
diff --git a/tests/phpunit/tests/rest-api.php b/tests/phpunit/tests/rest-api.php
index 1fe1b49540..b364a8af72 100644
--- a/tests/phpunit/tests/rest-api.php
+++ b/tests/phpunit/tests/rest-api.php
@@ -275,11 +275,15 @@ class Tests_REST_API extends WP_UnitTestCase {
 	 */
 	public function test_rest_url_generation() {
 		// In pretty permalinks case, we expect a path of wp-json/ with no query.
-		update_option( 'permalink_structure', '/%year%/%monthnum%/%day%/%postname%/' );
+		$this->set_permalink_structure( '/%year%/%monthnum%/%day%/%postname%/' );
 		$this->assertEquals( 'http://' . WP_TESTS_DOMAIN . '/wp-json/', get_rest_url() );
 
-		update_option( 'permalink_structure', '' );
+		// In index permalinks case, we expect a path of index.php/wp-json/ with no query.
+		$this->set_permalink_structure( '/index.php/%year%/%monthnum%/%day%/%postname%/' );
+		$this->assertEquals( 'http://' . WP_TESTS_DOMAIN . '/index.php/wp-json/', get_rest_url() );
+
 		// In non-pretty case, we get a query string to invoke the rest router.
+		$this->set_permalink_structure( '' );
 		$this->assertEquals( 'http://' . WP_TESTS_DOMAIN . '/?rest_route=/', get_rest_url() );
 
 	}