diff --git a/src/wp-includes/rewrite.php b/src/wp-includes/rewrite.php
index a03754f272..2666ff6f97 100644
--- a/src/wp-includes/rewrite.php
+++ b/src/wp-includes/rewrite.php
@@ -273,7 +273,10 @@ function add_feed( $feedname, $function ) {
  */
 function flush_rewrite_rules( $hard = true ) {
 	global $wp_rewrite;
-	$wp_rewrite->flush_rules( $hard );
+
+	if ( is_callable( array( $wp_rewrite, 'flush_rules' ) ) ) {
+		$wp_rewrite->flush_rules( $hard );
+	}
 }
 
 /**