diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index fd6264344..369d80efa 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1337,7 +1337,7 @@ function wp_nonce_ays($action) {
 function wp_die( $message, $title = '' ) {
 	global $wp_locale;
 
-	if ( is_wp_error( $message ) ) {
+	if ( function_exists( 'is_wp_error' ) && is_wp_error( $message ) ) {
 		if ( empty($title) ) {
 			$error_data = $message->get_error_data();
 			if ( is_array($error_data) && isset($error_data['title']) )