diff --git a/CHANGELOG.md b/CHANGELOG.md
index d3e9f6c2..983c5e56 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ In order to read more about upgrading and BC breaks have a look at the [UPGRADE
 ## 5.1.1
 
 + [#410](https://github.com/luyadev/luya-module-cms/pull/410) Disabled sorting functionality for the "group" extra field in the block CRUD interface due to an exception being thrown. This issue occurred because the field is declared as an `extraAttribute`.
++ [#409](https://github.com/luyadev/luya-module-cms/issues/409) Implemented a new validation check to prevent slug duplication within the same language and navigation hierarchy when creating a new page. This enhancement ensures unique page identification and avoids conflicts in site structure.
 
 ## 5.1.0 (7. February 2024)
 
diff --git a/src/models/NavItem.php b/src/models/NavItem.php
index 2a6aa496..007ed741 100644
--- a/src/models/NavItem.php
+++ b/src/models/NavItem.php
@@ -256,6 +256,9 @@ public function verifyAlias($alias, $langId)
             return false;
         }
 
+        // when no parent nav id is given, the post value is `null` therefore we have the explicit set the value to `0`.
+        $parentNavId = $this->parent_nav_id ?: 0;
+
         /**
          * Group by website_id
          * @since 4.0.0
@@ -263,7 +266,7 @@ public function verifyAlias($alias, $langId)
         $exists = static::find()
             ->leftJoin('cms_nav', 'cms_nav_item.nav_id=cms_nav.id')
             ->leftJoin('cms_nav_container', 'cms_nav.nav_container_id=cms_nav_container.id')
-            ->where(['cms_nav_item.alias' => $alias, 'cms_nav_item.lang_id' => $langId, 'cms_nav.parent_nav_id' => $this->parent_nav_id])
+            ->where(['cms_nav_item.alias' => $alias, 'cms_nav_item.lang_id' => $langId, 'cms_nav.parent_nav_id' => $parentNavId])
             ->groupBy('cms_nav_container.website_id')
             ->exists();
         if ($exists) {