diff --git a/src/Plugin/Validation/Constraint/UsernameFormatConstraint.php b/src/Plugin/Validation/Constraint/UsernameFormatConstraint.php
index a230784..8602e9a 100644
--- a/src/Plugin/Validation/Constraint/UsernameFormatConstraint.php
+++ b/src/Plugin/Validation/Constraint/UsernameFormatConstraint.php
@@ -14,39 +14,10 @@ use Symfony\Component\Validator\Constraint;
  */
 class UsernameFormatConstraint extends Constraint {
 
-  /**
-   * Message when the username begins with a space.
-   *
-   * @var string
-   */
-  public $beginSpace = 'The username cannot begin with a space.';
-
-  /**
-   * Message when the username ends with a space.
-   *
-   * @var string
-   */
-  public $endSpace = 'The username cannot end with a space.';
-
-  /**
-   * Message when the username contains multiple spaces in a row.
-   *
-   * @var string
-   */
-  public $multipleSpace = 'The username cannot contain multiple spaces in a row.';
-
-  /**
-   * Message when the username contains an invalid character.
-   *
-   * @var string
-   */
-  public $invalidCharacter = "The username contains punctuation, only periods, hyphens, apostrophes, and underscores are allowed.";
-
-  /**
-   * Message when the username contains an illegal character.
-   *
-   * @var string
-   */
-  public $illegalCharacter = "The username contains an illegal character.";
+  public $spaceBeginMessage = 'The username cannot begin with a space.';
+  public $spaceEndMessage = 'The username cannot end with a space.';
+  public $multipleSpacesMessage = 'The username cannot contain multiple spaces in a row.';
+  public $illegalMessage = 'The username contains an illegal character.';
+  public $tooLongMessage = 'The username %name is too long: it must be %max characters or less.';
 
 }
diff --git a/src/Plugin/Validation/Constraint/UsernameFormatConstraintValidator.php b/src/Plugin/Validation/Constraint/UsernameFormatConstraintValidator.php
index b235578..9708dfd 100644
--- a/src/Plugin/Validation/Constraint/UsernameFormatConstraintValidator.php
+++ b/src/Plugin/Validation/Constraint/UsernameFormatConstraintValidator.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\do_username\Plugin\Validation\Constraint;
 
+use Drupal\user\UserInterface;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidator;
 
@@ -13,21 +14,43 @@ class UsernameFormatConstraintValidator extends ConstraintValidator {
   /**
    * {@inheritdoc}
    */
-  public function validate($item, Constraint $constraint) {
-    if (substr($item->value, 0, 1) == ' ') {
-      $this->context->addViolation($constraint->beginSpace, ['%value' => $item->value]);
+  public function validate($items, Constraint $constraint) {
+    $name = $items->first()->value;
+    if (substr($name, 0, 1) == ' ') {
+      $this->context->addViolation($constraint->spaceBeginMessage);
     }
-    if (substr($item->value, -1) == ' ') {
-      $this->context->addViolation($constraint->endSpace, ['%value' => $item->value]);
+    if (substr($name, -1) == ' ') {
+      $this->context->addViolation($constraint->spaceEndMessage);
     }
-    if (strpos($item->value, '  ') !== FALSE) {
-      $this->context->addViolation($constraint->multipleSpace, ['%value' => $item->value]);
+    if (strpos($name, '  ') !== FALSE) {
+      $this->context->addViolation($constraint->multipleSpacesMessage);
     }
-    if (preg_match('/[^\\x{80}-\\x{F7} a-z0-9@+_.\'-]/i', $item->value)) {
-      $this->context->addViolation($constraint->invalidCharacter, ['%value' => $item->value]);
+    if (preg_match('/[^\x{80}-\x{F7} a-z0-9@+_.\'-]/i', $name)
+      || preg_match(
+      // Non-printable ISO-8859-1 + NBSP
+        '/[\x{80}-\x{A0}' .
+        // Soft-hyphen
+        '\x{AD}' .
+        // Various space characters
+        '\x{2000}-\x{200F}' .
+        // Bidirectional text overrides
+        '\x{2028}-\x{202F}' .
+        // Various text hinting characters
+        '\x{205F}-\x{206F}' .
+        // Byte order mark
+        '\x{FEFF}' .
+        // Full-width latin
+        '\x{FF01}-\x{FF60}' .
+        // Replacement characters
+        '\x{FFF9}-\x{FFFD}' .
+        // NULL byte and control characters
+        '\x{0}-\x{1F}]/u',
+        $name)
+    ) {
+      $this->context->addViolation($constraint->illegalMessage);
     }
-    if (preg_match('/[\\x{80}-\\x{A0}' . '\\x{AD}' . '\\x{2000}-\\x{200F}' . '\\x{2028}-\\x{202F}' . '\\x{205F}-\\x{206F}' . '\\x{FEFF}' . '\\x{FF01}-\\x{FF60}' . '\\x{FFF9}-\\x{FFFD}' . '\\x{0}-\\x{1F}]/u', $item->value)) {
-      $this->context->addViolation($constraint->illegalCharacter, ['%value' => $item->value]);
+    if (mb_strlen($name) > UserInterface::USERNAME_MAX_LENGTH) {
+      $this->context->addViolation($constraint->tooLongMessage, ['%name' => $name, '%max' => UserInterface::USERNAME_MAX_LENGTH]);
     }
   }