diff --git a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
index 9e18f71a4f3ac02822329de40db06314f15bf635..3b43dee3f47170f8481b111076d43d5b32e38048 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
@@ -174,7 +174,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#type' => 'textfield',
       '#title' => $this->t('Username'),
       '#maxlength' => USERNAME_MAX_LENGTH,
-      '#description' => $this->t('Spaces are allowed; punctuation is not allowed except for periods, hyphens, and underscores.'),
+      '#description' => $this->t("Several special characters are allowed, including space, period (.), hyphen (-), apostrophe ('), underscore (_), and the @ sign."),
       '#required' => TRUE,
       '#attributes' => array('class' => array('username')),
     );
diff --git a/core/modules/user/src/AccountForm.php b/core/modules/user/src/AccountForm.php
index 4b10f19ba0c94fb9c2c1e9d5cbddb014c73a6151..289a1a9070c66b82d6a9f896d6a49eae31e33150 100644
--- a/core/modules/user/src/AccountForm.php
+++ b/core/modules/user/src/AccountForm.php
@@ -104,7 +104,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#type' => 'textfield',
       '#title' => $this->t('Username'),
       '#maxlength' => USERNAME_MAX_LENGTH,
-      '#description' => $this->t('Spaces are allowed; punctuation is not allowed except for periods, hyphens, apostrophes, and underscores.'),
+      '#description' => $this->t("Several special characters are allowed, including space, period (.), hyphen (-), apostrophe ('), underscore (_), and the @ sign."),
       '#required' => TRUE,
       '#attributes' => array(
         'class' => array('username'),