diff --git a/src/ServerResponse.php b/src/ServerResponse.php
index 5982fbc7ae4b4e1ab5103fb90b3376da70dfa3da..9e722e1e229df7f9039111232cf0cd9f0e37c4c5 100644
--- a/src/ServerResponse.php
+++ b/src/ServerResponse.php
@@ -89,7 +89,7 @@ class ServerResponse extends Response implements ServerResponseInterface
         }
 
         if ($sameSite) {
-            $headerLine .= '; SameSite';
+            $headerLine .= '; SameSite=strict';
         }
 
         $this->addHeader('Set-Cookie', $headerLine);