Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 37299)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -6326,7 +6326,7 @@
 		$remote_source = preg_replace( "/<\/*(h1|h2|h3|h4|h5|h6|p|th|td|li|dt|dd|pre|caption|input|textarea|button|body)[^>]*>/", "\n\n", $remote_source );
 
 		preg_match( '|<title>([^<]*?)</title>|is', $remote_source, $matchtitle );
-		$title = $matchtitle[1];
+		$title = !empty( $matchtitle[1] ) ? $matchtitle[1] : '';
 		if ( empty( $title ) )
 			return $this->pingback_error( 32, __('We cannot find a title on that page.' ) );