diff --git a/core/lib/Drupal/Component/Utility/Unicode.php b/core/lib/Drupal/Component/Utility/Unicode.php
index 6bbece6..3ae7b35 100644
--- a/core/lib/Drupal/Component/Utility/Unicode.php
+++ b/core/lib/Drupal/Component/Utility/Unicode.php
@@ -123,7 +123,7 @@ public static function getStatus() {
    * @param int $status
    *   The new status of multibyte support.
    *
-   * @deprecated in Drupal 8.0.0, will be removed before Drupal 9.0.0. In Drupal
+   * @deprecated in Drupal 8.3.0, will be removed before Drupal 9.0.0. In Drupal
    *   9 there will be no way to set the status and in Drupal 8 this ability has
    *   been removed.
    */
@@ -264,6 +264,9 @@ public static function truncateBytes($string, $len) {
    *
    * @return int
    *   The length of the string.
+   *
+   * @deprecated in Drupal 8.3.0, will be removed before Drupal 9.0.0. Use
+   *   mb_strlen() instead.
    */
   public static function strlen($text) {
     return mb_strlen($text);
@@ -277,6 +280,9 @@ public static function strlen($text) {
    *
    * @return string
    *   The string in uppercase.
+   *
+   * @deprecated in Drupal 8.3.0, will be removed before Drupal 9.0.0. Use
+   *   mb_strtoupper() instead.
    */
   public static function strtoupper($text) {
     return mb_strtoupper($text);
@@ -290,6 +296,9 @@ public static function strtoupper($text) {
    *
    * @return string
    *   The string in lowercase.
+   *
+   * @deprecated in Drupal 8.3.0, will be removed before Drupal 9.0.0. Use
+   *   mb_strtolower() instead.
    */
   public static function strtolower($text) {
     return mb_strtolower($text);
@@ -358,9 +367,12 @@ public static function ucwords($text) {
    *
    * @return string
    *   The shortened string.
+   *
+   * @deprecated in Drupal 8.3.0, will be removed before Drupal 9.0.0. Use
+   *   mb_substr() instead.
    */
   public static function substr($text, $start, $length = NULL) {
-    return $length === NULL ? mb_substr($text, $start) : mb_substr($text, $start, $length);
+    return mb_substr($text, $start, $length);
   }
 
   /**
@@ -585,6 +597,9 @@ public static function validateUtf8($text) {
    *   The position where $needle occurs in $haystack, always relative to the
    *   beginning (independent of $offset), or FALSE if not found. Note that
    *   a return value of 0 is not the same as FALSE.
+   *
+   * @deprecated in Drupal 8.3.0, will be removed before Drupal 9.0.0. Use
+   *   mb_strpos() instead.
    */
   public static function strpos($haystack, $needle, $offset = 0) {
     return mb_strpos($haystack, $needle, $offset);