diff --git a/wp-includes/load.php b/wp-includes/load.php
index 311643f47f..f036a5a2b9 100644
--- a/wp-includes/load.php
+++ b/wp-includes/load.php
@@ -568,6 +568,9 @@ function is_admin() {
  * @return bool True if multisite is enabled, false otherwise.
  */
 function is_multisite() {
+	if ( defined( 'MULTISITE' ) && ! MULTISITE )
+		return false;
+
 	if ( ( defined( 'MULTISITE' ) && MULTISITE ) || defined( 'VHOST' ) || defined( 'SUNRISE' ) )
 		return true;
 
diff --git a/wp-settings.php b/wp-settings.php
index 8437cfb38c..197ecae177 100644
--- a/wp-settings.php
+++ b/wp-settings.php
@@ -85,6 +85,8 @@ require( ABSPATH . WPINC . '/pomo/mo.php' );
 if ( is_multisite() ) {
 	require( ABSPATH . WPINC . '/ms-blogs.php' );
 	require( ABSPATH . WPINC . '/ms-settings.php' );
+} elseif ( ! defined( 'MULTISITE' ) ) {
+	define( 'MULTISITE', false );
 }
 
 // Stop most of WordPress from being loaded if we just want the basics.