diff -r 003acf02d416 tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c	Thu Jan 20 17:04:06 2011 +0000
+++ b/tools/libxl/xl_cmdimpl.c	Fri Jan 21 17:11:10 2011 +0100
@@ -170,6 +170,10 @@
         exit(2);
     }
     common_domname = was_name ? p : libxl_domid_to_name(&ctx, domid);
+    if (common_domname == NULL) {
+    	fprintf(stderr, "%d is not a valid domain\n", domid);
+    	exit(2);
+    }
 }
 
 static int acquire_lock(void)