Index: parsers.php
===================================================================
--- parsers.php	(revision 585925)
+++ parsers.php	(working copy)
@@ -72,7 +72,10 @@
 			return new WP_Error( 'WXR_parse_error', __( 'This does not appear to be a WXR file, missing/invalid WXR version number', 'wordpress-importer' ) );
 
 		$base_url = $xml->xpath('/rss/channel/wp:base_site_url');
-		$base_url = (string) trim( $base_url[0] );
+		if ( $base_url ) 
+			$base_url = (string) trim( $base_url[0] );
+		else
+			$base_url = false;
 
 		$namespaces = $xml->getDocNamespaces();
 		if ( ! isset( $namespaces['wp'] ) )