Index: wp-includes/ms-settings.php
===================================================================
--- wp-includes/ms-settings.php	(revision 17644)
+++ wp-includes/ms-settings.php	(working copy)
@@ -18,8 +18,8 @@
 require( ABSPATH . WPINC . '/ms-load.php' );
 require( ABSPATH . WPINC . '/ms-default-constants.php' );
 
-if ( defined( 'SUNRISE' ) )
-	include_once( WP_CONTENT_DIR . '/sunrise.php' );
+/** Load /wp-content/sunrise.php for Multisite */
+wp_load_sunrise();
 
 /** Check for and define SUBDOMAIN_INSTALL and the deprecated VHOST constant. */
 ms_subdomain_constants();
Index: wp-settings.php
===================================================================
--- wp-settings.php	(revision 17644)
+++ wp-settings.php	(working copy)
@@ -90,6 +90,10 @@
 	define( 'MULTISITE', false );
 }
 
+// Load /wp-content/sunrise.php for single site installations
+if ( ! MULTISITE )
+	wp_load_sunrise();
+
 // Stop most of WordPress from being loaded if we just want the basics.
 if ( SHORTINIT )
 	return false;
@@ -317,4 +321,23 @@
  * @since 3.0.0
  */
 do_action('wp_loaded');
+
+/**
+ * Load /wp-content/sunrise.php if the constant SUNRISE has been defined and the file exists, die with an error messsage if not.
+ *
+ * @since 3.2.0
+ *
+ * @uses SUNRISE constant Checks to see if it is set in order to load /wp-content/sunrise.php.
+ * @uses /wp-content/sunrise.php Loads /wp-content/sunrise.php if SUNRISE constant is defined.
+ *
+ */
+function wp_load_sunrise() {
+	if ( defined( 'SUNRISE' ) ) {
+		$sunrise_php = WP_CONTENT_DIR . '/sunrise.php';
+		if ( !file_exists( $sunrise_php ) )
+			wp_die( __( "The constant SUNRISE was defined but the file [{$sunrise_php}] does not exist." ) );
+		else
+			include_once( $sunrise_php );
+	}
+}
 ?>