diff --git a/doc/09-object-types.md b/doc/09-object-types.md
index 6dda8c91d..e60204749 100644
--- a/doc/09-object-types.md
+++ b/doc/09-object-types.md
@@ -1760,7 +1760,7 @@ Configuration Attributes:
   Name                      | Type                  | Description
   --------------------------|-----------------------|----------------------------------
   endpoints                 | Array of object names | **Optional.** Array of endpoint names located in this zone.
-  parent                    | Object name           | **Optional.** The name of the parent zone.
+  parent                    | Object name           | **Optional.** The name of the parent zone. (Do not specify a global zone)
   global                    | Boolean               | **Optional.** Whether configuration files for this zone should be [synced](06-distributed-monitoring.md#distributed-monitoring-global-zone-config-sync) to all endpoints. Defaults to `false`.
 
 Zone objects cannot currently be created with the API.
diff --git a/doc/16-upgrading-icinga-2.md b/doc/16-upgrading-icinga-2.md
index 83b4bd3ec..bc15462bb 100644
--- a/doc/16-upgrading-icinga-2.md
+++ b/doc/16-upgrading-icinga-2.md
@@ -91,6 +91,21 @@ sending the recovery notification.
 
 More details can be found in [this PR](https://github.com/Icinga/icinga2/pull/6527).
 
+### Stricter configuration validation
+
+Some config errors are now fatal. While it never worked before, icinga2 refuses to start now!
+
+For example the following started to give a fatal error in 2.10:
+
+```
+  object Zone "XXX" {
+    endpoints = [ "master-server" ]
+    parent = "global-templates"
+  }
+```
+
+```critical/config: Error: Zone 'XXX' can not have a global zone as parent.```
+
 ## Upgrading to v2.9 <a id="upgrading-to-2-9"></a>
 
 ### Deprecation and Removal Notes <a id="upgrading-to-2-9-deprecation-removal-notes"></a>