diff --git a/src/Event/Application/values/OS.php b/src/Event/Application/values/OS.php
index a3799a2ad9c..74686c644a0 100644
--- a/src/Event/Application/values/OS.php
+++ b/src/Event/Application/values/OS.php
@@ -14,12 +14,12 @@
 
 class OS
 {
-    public function asString()
+    public function asString(): string
     {
         return PHP_OS;
     }
 
-    public function family()
+    public function family(): string
     {
         return PHP_OS_FAMILY;
     }