diff --git a/src/Ratchet/Session/Storage/VirtualSessionStorage.php b/src/Ratchet/Session/Storage/VirtualSessionStorage.php
index daa10bba..b92cf076 100644
--- a/src/Ratchet/Session/Storage/VirtualSessionStorage.php
+++ b/src/Ratchet/Session/Storage/VirtualSessionStorage.php
@@ -25,7 +25,7 @@ public function __construct(\SessionHandlerInterface $handler, $sessionId, Handl
     /**
      * {@inheritdoc}
      */
-    public function start() {
+    public function start() : bool {
         if ($this->started && !$this->closed) {
             return true;
         }