diff --git a/src/Symfony/Bridge/Monolog/Handler/ChromePhpHandler.php b/src/Symfony/Bridge/Monolog/Handler/ChromePhpHandler.php
index 059dc539e1681..1fa698a9390b6 100644
--- a/src/Symfony/Bridge/Monolog/Handler/ChromePhpHandler.php
+++ b/src/Symfony/Bridge/Monolog/Handler/ChromePhpHandler.php
@@ -59,7 +59,7 @@ protected function sendHeader($header, $content): void
             return;
         }
 
-        if ($this->response) {
+        if (isset($this->response)) {
             $this->response->headers->set($header, $content);
         } else {
             $this->headers[$header] = $content;