diff --git a/Tests/ClientTest.php b/Tests/ClientTest.php
index ab6d1185..a21a9481 100644
--- a/Tests/ClientTest.php
+++ b/Tests/ClientTest.php
@@ -621,6 +621,9 @@ public function testRestart()
         $this->assertEquals([], $client->getCookieJar()->all(), '->restart() clears the cookies');
     }
 
+    /**
+     * @runInSeparateProcess
+     */
     public function testInsulatedRequests()
     {
         $client = new TestClient();