diff --git a/src/Symfony/Component/HttpFoundation/Cookie.php b/src/Symfony/Component/HttpFoundation/Cookie.php
index 492c6fbe75..5ea881c6e3 100644
--- a/src/Symfony/Component/HttpFoundation/Cookie.php
+++ b/src/Symfony/Component/HttpFoundation/Cookie.php
@@ -77,6 +77,10 @@ class Cookie
         $this->httpOnly = (bool) $httpOnly;
         $this->raw = (bool) $raw;
 
+        if (null !== $sameSite) {
+            $sameSite = strtolower($sameSite);
+        }
+
         if (!in_array($sameSite, array(self::SAMESITE_LAX, self::SAMESITE_STRICT, null), true)) {
             throw new \InvalidArgumentException('The "sameSite" parameter value is not valid.');
         }
diff --git a/src/Symfony/Component/HttpFoundation/Tests/CookieTest.php b/src/Symfony/Component/HttpFoundation/Tests/CookieTest.php
index 3986a7e8f8..ad6d3f508c 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/CookieTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/CookieTest.php
@@ -180,4 +180,10 @@ class CookieTest extends TestCase
         $this->assertTrue($cookie->isRaw());
         $this->assertEquals('foo=b+a+r; path=/', (string) $cookie);
     }
+
+    public function testSameSiteAttributeIsCaseInsensitive()
+    {
+        $cookie = new Cookie('foo', 'bar', 0, '/', null, false, true, false, 'Lax');
+        $this->assertEquals('lax', $cookie->getSameSite());
+    }
 }