diff --git a/code/Controller/AssetAdmin.php b/code/Controller/AssetAdmin.php
index 5361ebe5a..86ac05769 100644
--- a/code/Controller/AssetAdmin.php
+++ b/code/Controller/AssetAdmin.php
@@ -206,7 +206,7 @@ public function init()
     /**
      * Returns configuration required by the client app
      */
-    public function getClientConfig()
+    public function getClientConfig(): array
     {
         $baseLink = $this->Link();
         $validator = $this->getUpload()->getValidator();
diff --git a/code/Controller/AssetAdminOpen.php b/code/Controller/AssetAdminOpen.php
index fa6ccbfa1..54522e29f 100644
--- a/code/Controller/AssetAdminOpen.php
+++ b/code/Controller/AssetAdminOpen.php
@@ -81,7 +81,7 @@ public function init()
     /**
      * Returns configuration required by the client app
      */
-    public function getClientConfig()
+    public function getClientConfig(): array
     {
         return array_merge(parent::getClientConfig(), [
             'reactRouter' => true,