Index: ms-functions.php
===================================================================
--- ms-functions.php	(revision 14521)
+++ ms-functions.php	(working copy)
@@ -320,6 +320,11 @@
 	if ( empty($path) )
 		$path = '/';
 
+	// Check if we're in a list of forbidden paths
+	$reserved_blognames = array( 'page', 'comments', 'blog', 'wp-admin', 'wp-includes', 'wp-content', 'files', 'feed' );
+	if( array_key_exists($path,$reserved_blognames) )
+	    return __( 'Error: Forbidden site name.' );
+
 	// Check if the domain has been used already. We should return an error message.
 	if ( domain_exists($domain, $path, $site_id) )
 		return __( 'Error: Site URL already taken.' );