Index: wp-includes/capabilities.php
===================================================================
--- wp-includes/capabilities.php	(revision 21549)
+++ wp-includes/capabilities.php	(working copy)
@@ -1423,10 +1423,12 @@
  * @return bool True if the user is a site admin.
  */
 function is_super_admin( $user_id = false ) {
-	if ( ! $user_id )
-		$user_id = get_current_user_id();
+	if ( ! $user_id || get_current_user_id() == $user_id )
+		$user = wp_get_current_user();
+	else
+		$user = get_userdata( $user_id );
 
-	if ( ! $user = get_userdata( $user_id ) )
+	if ( ! $user )
 		return false;
 
 	if ( is_multisite() ) {