diff --git a/src/Server.php b/src/Server.php
index d34ab2b..d24f75c 100644
--- a/src/Server.php
+++ b/src/Server.php
@@ -202,7 +202,7 @@ public function onMessage($server, $frame): void
         $instance = $this->container->get($fdObj->class);
 
         if (! $instance instanceof OnMessageInterface) {
-            $this->logger->warning("{$instance} is not instanceof " . OnMessageInterface::class);
+            $this->logger->warning($instance::class . ' is not instanceof ' . OnMessageInterface::class);
             return;
         }