diff --git a/lib/config.py b/lib/config.py
index e24a17d3d3e154bd63b22824b12a314d63e5fe4a..ef2aedbec3d9ed91f6cce39c5a6e2218ce340aea 100644
--- a/lib/config.py
+++ b/lib/config.py
@@ -677,7 +677,7 @@ class ConfigWriter:
     """Bump up the serial number of the config.
 
     """
-    self._config_data.cluster.serial_no += 1
+    self._config_data.serial_no += 1
 
   def _OpenConfig(self):
     """Read the config data from disk.
@@ -805,7 +805,8 @@ class ConfigWriter:
 
     self._config_data = objects.ConfigData(nodes={node: nodeconfig},
                                            instances={},
-                                           cluster=globalconfig)
+                                           cluster=globalconfig,
+                                           serial_no=1)
     self._WriteConfig()
 
   @locking.ssynchronized(_config_lock, shared=1)