diff --git a/common/oatbox/service/ServiceManager.php b/common/oatbox/service/ServiceManager.php
index a45b75934..6734c9872 100644
--- a/common/oatbox/service/ServiceManager.php
+++ b/common/oatbox/service/ServiceManager.php
@@ -139,7 +139,7 @@ private function tryAutowiring($serviceId, $serviceKey)
      * (non-PHPdoc)
      * @see ContainerInterface::has()
      */
-    public function has($serviceKey)
+    public function has($serviceKey): bool
     {
         if (isset($this->services[$serviceKey])) {
             return true;