diff --git a/tests/system/HTTP/DownloadResponseTest.php b/tests/system/HTTP/DownloadResponseTest.php
index f0c9b3024f6d..538575ab4d9d 100644
--- a/tests/system/HTTP/DownloadResponseTest.php
+++ b/tests/system/HTTP/DownloadResponseTest.php
@@ -50,9 +50,10 @@ public function testSetDateRemembersDateInUTC()
     {
         $response = new DownloadResponse('unit-test.txt', true);
 
-        $response->setDate(DateTime::createFromFormat('Y-m-d', '2000-03-10'));
+        $datetime = DateTime::createFromFormat('!Y-m-d', '2000-03-10');
+        $response->setDate($datetime);
 
-        $date = DateTime::createFromFormat('Y-m-d', '2000-03-10');
+        $date = clone $datetime;
         $date->setTimezone(new DateTimeZone('UTC'));
 
         $header = $response->getHeaderLine('Date');
diff --git a/tests/system/HTTP/ResponseTest.php b/tests/system/HTTP/ResponseTest.php
index f66be1513004..4185082ee47c 100644
--- a/tests/system/HTTP/ResponseTest.php
+++ b/tests/system/HTTP/ResponseTest.php
@@ -144,9 +144,10 @@ public function testSetDateRemembersDateInUTC()
     {
         $response = new Response(new App());
 
-        $response->setDate(DateTime::createFromFormat('Y-m-d', '2000-03-10'));
+        $datetime = DateTime::createFromFormat('!Y-m-d', '2000-03-10');
+        $response->setDate($datetime);
 
-        $date = DateTime::createFromFormat('Y-m-d', '2000-03-10');
+        $date = clone $datetime;
         $date->setTimezone(new DateTimeZone('UTC'));
 
         $header = $response->getHeaderLine('Date');