diff --git a/src/Symfony/Component/HttpKernel/DataCollector/RequestDataCollector.php b/src/Symfony/Component/HttpKernel/DataCollector/RequestDataCollector.php
index be08e305a2..9371748e3c 100644
--- a/src/Symfony/Component/HttpKernel/DataCollector/RequestDataCollector.php
+++ b/src/Symfony/Component/HttpKernel/DataCollector/RequestDataCollector.php
@@ -298,10 +298,11 @@ class RequestDataCollector extends DataCollector implements EventSubscriberInter
             } elseif ($expires instanceof \DateTime) {
                 $expires = $expires->getTimestamp();
             } else {
-                $expires = strtotime($expires);
-                if (false === $expires || -1 == $expires) {
-                    throw new \InvalidArgumentException(sprintf('The "expires" cookie parameter is not valid.', $expires));
+                $tmp = strtotime($expires);
+                if (false === $tmp || -1 == $tmp) {
+                    throw new \InvalidArgumentException(sprintf('The "expires" cookie parameter is not valid (%s).', $expires));
                 }
+                $expires = $tmp;
             }
 
             $cookie .= '; expires='.str_replace('+0000', '', \DateTime::createFromFormat('U', $expires, new \DateTimeZone('GMT'))->format('D, d-M-Y H:i:s T'));