diff --git a/core/lib/Drupal/Component/Utility/Unicode.php b/core/lib/Drupal/Component/Utility/Unicode.php
index 5432f39601..611d0f99e2 100644
--- a/core/lib/Drupal/Component/Utility/Unicode.php
+++ b/core/lib/Drupal/Component/Utility/Unicode.php
@@ -599,10 +599,8 @@ public static function strcasecmp($str1 , $str2) {
    * - According to RFC 2047, we split long lines using CLRF SPACE as separator.
    * - PHP's mail() function (http://php.net/manual/en/function.mail.php) used
    *   to have an explicit restriction that subject lines could not contain LF.
-   *   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.
+   *   This restriction has been lifted since november 2009 or earlier, so we
+   *   assume that systems having problems with them are extinct by now.
    *
    * @param string $string
    *   The header to encode.