diff --git a/core/lib/Drupal/Component/Utility/Unicode.php b/core/lib/Drupal/Component/Utility/Unicode.php
index 3eb51f3..df5bb39 100644
--- a/core/lib/Drupal/Component/Utility/Unicode.php
+++ b/core/lib/Drupal/Component/Utility/Unicode.php
@@ -602,8 +602,7 @@ public static function strcasecmp($str1 , $str2) {
    *   This restriction has been lifted since november 2009 or earlier, but
    *   occasional problem reports have still popped up about a system not being
    *   able to deal with "\n" in subject lines, whose source (php or mailer) was
-   *   not confirmed. See https://www.drupal.org/node/300387#comment-7701323
-   *   and please report details there in case of problems.
+   *   not confirmed.
    *
    * @param string $string
    *   The header to encode.
diff --git a/core/tests/Drupal/Tests/Component/Utility/UnicodeTest.php b/core/tests/Drupal/Tests/Component/Utility/UnicodeTest.php
index e9ca951..17c6fa2 100644
--- a/core/tests/Drupal/Tests/Component/Utility/UnicodeTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/UnicodeTest.php
@@ -84,6 +84,7 @@ public function testMimeHeader($value, $encoded) {
    */
   public function providerTestMimeHeader() {
     return array(
+      array('tést.txt', '=?UTF-8?B?dMOpc3QudHh0?='),
       // Simple ASCII characters.
       array('ASCII', 'ASCII'),
       // Long ASCII string (more than 45 bytes).
@@ -94,6 +95,8 @@ public function providerTestMimeHeader() {
       // longer than 45 bytes: converts into two encoded chunks separated by
       // CLRF + space, according to http://www.rfc-editor.org/rfc/rfc2047.txt
       array('1234567890abcdefghij1234567890abcdefghij1234à', "=?UTF-8?B?MTIzNDU2Nzg5MGFiY2RlZmdoaWoxMjM0NTY3ODkwYWJjZGVmZ2hpajEyMzQ=?=\r\n =?UTF-8?B?w6A=?="),
+      // ASCII string including a LF.
+      array("ASCII\nASCII", '=?UTF-8?B?QVNDSUkKQVNDSUk=?='),
     );
   }