diff --git a/src/Symfony/Component/HttpFoundation/Response.php b/src/Symfony/Component/HttpFoundation/Response.php
index d50840bd7b..dbc82d1b61 100644
--- a/src/Symfony/Component/HttpFoundation/Response.php
+++ b/src/Symfony/Component/HttpFoundation/Response.php
@@ -306,7 +306,7 @@ class Response
             $obStatus = ob_get_status(1);
             while (($level = ob_get_level()) > 0 && $level !== $previous) {
                 $previous = $level;
-                if ($obStatus[$level - 1] && $obStatus[$level - 1]['del']) {
+                if ($obStatus[$level - 1] && isset($obStatus[$level - 1]['del']) && $obStatus[$level - 1]['del']) {
                     ob_end_flush();
                 }
             }