diff -Naur a/x11.vapi b/x11.vapi
--- a/x11.vapi	2011-04-04 22:49:53.000000000 +0200
+++ b/x11.vapi	2011-04-04 20:13:27.000000000 +0200
@@ -76,7 +76,7 @@
 		public unowned Screen screen_by_id (int screen_number);
 
 		[CCode (cname = "DisplayString")]
-		public string display_string ();
+		public unowned string display_string ();
 
 		[CCode (cname = "XQLength")]
 		public int event_queue_length ();