diff --git a/bhl.inc.php b/bhl.inc.php
index dff205f..ecd6785 100644
--- a/bhl.inc.php
+++ b/bhl.inc.php
@@ -300,7 +300,10 @@ function bhl_ast_post_proc($res_file, $post_proc_file)
 {
   $res = new BhlAstProcResult();
   $res->res_file = $res_file;
-  $data = config_msgpack_unpack(ensure_read($post_proc_file));
+  $data = ensure_read($post_proc_file);
+  if(!$data)
+    return $res;
+  $data = config_msgpack_unpack($data);
   if(!$data)
     return $res;