diff --git a/_config/extensions.yml b/_config/extensions.yml
index fdc21e0..4d60372 100644
--- a/_config/extensions.yml
+++ b/_config/extensions.yml
@@ -4,10 +4,8 @@ Only:
   classexists: '\SilverStripe\Subsites\Model\Subsite'
 ---
 SilverStripe\Subsites\Model\Subsite:
-  has_many:
-    - MenuSets => 'Heyday\MenuManager\MenuSet'
-  cascade_deletes:
-    - MenuSets
+  extensions:
+    - Heyday\MenuManager\Extensions\SubsiteExtension
 Heyday\MenuManager\MenuAdmin:
   extensions:
     - SilverStripe\Subsites\Extensions\SubsiteMenuExtension
diff --git a/src/Extensions/MenuSubsiteExtension.php b/src/Extensions/MenuSubsiteExtension.php
index 4fdbe34..3a23288 100644
--- a/src/Extensions/MenuSubsiteExtension.php
+++ b/src/Extensions/MenuSubsiteExtension.php
@@ -6,7 +6,6 @@
 use SilverStripe\Forms\FieldList;
 use SilverStripe\Forms\HiddenField;
 use SilverStripe\ORM\DataExtension;
-use SilverStripe\Subsites\State\SubsiteState;
 
 if (!class_exists('\SilverStripe\Subsites\Model\Subsite') || !class_exists('\SilverStripe\Subsites\State\SubsiteState')) {
     return;
diff --git a/src/Extensions/SubsiteExtension.php b/src/Extensions/SubsiteExtension.php
new file mode 100644
index 0000000..cf6bf66
--- /dev/null
+++ b/src/Extensions/SubsiteExtension.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Heyday\MenuManager\Extensions;
+
+use Heyday\MenuManager\MenuSet;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\HiddenField;
+use SilverStripe\ORM\DataExtension;
+
+if (!class_exists('\SilverStripe\Subsites\Model\Subsite') || !class_exists('\SilverStripe\Subsites\State\SubsiteState')) {
+    return;
+}
+
+class SubsiteExtension extends DataExtension
+{
+    private static $has_many = [
+        'MenuSets' => MenuSet::class
+    ];
+
+    private static $cascade_deletes = [
+        'MenuSets'
+    ];
+
+    public function updateCMSFields(FieldList $fields)
+    {
+        $fields->removeByName('MenuSets');
+    }
+}