diff --git a/en/02_Developer_Guides/00_Model/09_Validation.md b/en/02_Developer_Guides/00_Model/09_Validation.md
index 12730e04..9cb7c21d 100644
--- a/en/02_Developer_Guides/00_Model/09_Validation.md
+++ b/en/02_Developer_Guides/00_Model/09_Validation.md
@@ -58,7 +58,7 @@ class MyObject extends DataObject
         'Postcode' => 'Varchar',
     ];
 
-    public function validate()
+    public function validate(): ValidationResult
     {
         $result = parent::validate();
 
diff --git a/en/08_Changelogs/6.0.0.md b/en/08_Changelogs/6.0.0.md
index 03f46aae..0a546173 100644
--- a/en/08_Changelogs/6.0.0.md
+++ b/en/08_Changelogs/6.0.0.md
@@ -31,6 +31,7 @@ title: 6.0.0 (unreleased)
 - [Bug fixes](#bug-fixes)
 - [API changes](#api-changes)
   - [Many renamed classes](#renamed-classes)
+  - [DataObject `validate()` signature change](#dataobject-validate)
   - [GraphQL removed from the CMS](#graphql-removed)
   - [`FormField` classes now use `FieldValidator` for validation](#formfield-validation)
   - [Most extension hook methods are now protected](#hooks-protected)
@@ -928,6 +929,33 @@ The following classes have been changed when code was moved to the `silverstripe
 |`SilverStripe\UserForms\Form\UserFormsRequiredFields`|[`SilverStripe\UserForms\Form\UserFormsRequiredFieldsValidator`](api:SilverStripe\UserForms\Form\UserFormsRequiredFieldsValidator)|
 |`Symbiote\AdvancedWorkflow\Forms\AWRequiredFields`|[`Symbiote\AdvancedWorkflow\Forms\AWRequiredFieldsValidator`](api:Symbiote\AdvancedWorkflow\Forms\AWRequiredFieldsValidator)|
 
+### DataObject `validate()` signature changed {#dataobject-validate}
+
+The method signature of the `validate()` method on `DataObject` has changed as it is now strongly typed. It now explicitly returns a [`ValidationResult`](api:SilverStripe\Core\Validation\ValidationResult). Previously the method still returned a `ValidationResult`, though this was not defined in the method signature.
+
+What this means is that you will now need to update the method sigature of any custom `validate()` methods you have in your `DataObject` subclasses to match the new signature.
+
+```php
+// app/src/Models/MyDataObject.php
+namespace App\Models;
+
+use SilverStripe\ORM\DataObject;
+use SilverStripe\Core\Validation\ValidationResult;
+
+class MyDataObject extends DataObject
+{
+    // ...
+    public function validate(): ValidationResult
+    {
+        $result = parent::validate();
+        if ($this->Title === 'Bad Title') {
+            $result->addError('Title cannot be "Bad Title"');
+        }
+        return $result;
+    }
+}
+```
+
 ### GraphQL removed from the CMS {#graphql-removed}
 
 > [!NOTE]