diff --git a/core/modules/user/lib/Drupal/user/Tests/UserEditTest.php b/core/modules/user/lib/Drupal/user/Tests/UserEditTest.php
index 6bf60bc..0a5fcd5 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserEditTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserEditTest.php
@@ -99,4 +99,30 @@ class UserEditTest extends WebTestBase {
     $this->drupalPost("user/$user1->uid/edit", array('mail' => ''), t('Save'));
     $this->assertRaw(t("The changes have been saved."));
   }
+
+  /**
+   * Check that existing users whose username matches another user's email
+   * address or vice versa are not forced to update their username or email
+   * address.
+   */
+  function testUserEditWithConflicts() {
+    $user_with_email = $this->drupalCreateUser();
+    $user_with_name = $this->drupalCreateUser();
+
+    // Change the second user's username to the same value as the first user's
+    // email address.
+    $user_with_name->name = $user_with_email->mail;
+    $user_with_name->save();
+
+    // Test that the first user can save their account with no errors.
+    $this->drupalLogin($user_with_email);
+    $this->drupalPost("user/$user_with_email->uid/edit", array(), t('Save'));
+    $this->assertText(t("The changes have been saved."), "The user does not need to change their username if it matches another user's email address.");
+    $this->drupalLogout();
+
+    // Test that the second user can save their account with no errors.
+    $this->drupalLogin($user_with_name);
+    $this->drupalPost("user/$user_with_name->uid/edit", array(), t('Save'));
+    $this->assertText(t("The changes have been saved."), "The user does not need to change their email address if it matches another user's username.");
+  }
 }
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserPasswordResetTest.php b/core/modules/user/lib/Drupal/user/Tests/UserPasswordResetTest.php
index 575409f..85a95ef 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserPasswordResetTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserPasswordResetTest.php
@@ -24,6 +24,60 @@ class UserPasswordResetTest extends WebTestBase {
   }
 
   /**
+   * Attempts to reset a password when an email address matches two accounts.
+   */
+  function testUserPasswordResetDuplicateUsers() {
+    // Don't require email validation for new accounts.
+    variable_set('user_email_verification', FALSE);
+
+    // Don't require admin approval for new accounts.
+    variable_set('user_register', USER_REGISTER_VISITORS);
+
+    // Create two users.
+    $user_with_email = $this->drupalCreateUser();
+    $user_with_name = $this->drupalCreateUser();
+
+    // Change the second user's username to the same value as the first user's
+    // email address.
+    $user_with_name->name = $user_with_email->mail;
+    $user_with_name->save();
+
+    // Try and reset based on the duplicated email.
+    $edit = array();
+    $edit['name'] = $user_with_email->mail;
+    $this->drupalPost('user/password', $edit, t('E-mail new password'));
+    // There should be a field prompting the user to pick and account.
+    $this->assertField('choose_account', 'User is prompted to pick an account when email matches two accounts.');
+    // We should be sure to not expose another user's email to the user.
+    $this->assertNoText($user_with_name->mail, "Duplicated user's email is not exposed to the other user.");
+
+    // Select the account with the username matching the entered email.
+    $edit = array();
+    $edit['choose_account'] = drupal_hash_base64(drupal_get_hash_salt() . $user_with_email->uid);
+    $this->drupalPost(NULL, $edit, t('E-mail new password'));
+    $this->assertText(t('Further instructions have been sent to your e-mail address.'), 'User is notified that password reset was sent.');
+
+    // Make sure that right user was sent a reset email.
+    $this->assertEqual(count($this->drupalGetMails(array('key' => 'password_reset', 'to' => $user_with_email->mail))), 1, 'The right user was sent a password reset mail.');
+    // Make sure that the other user was not sent an email.
+    $this->assertEqual(count($this->drupalGetMails(array('key' => 'password_reset', 'to' => $user_with_name->mail))), 0, 'The other user was not sent a password reset mail.');
+
+    // If the user is logged in, they should not have to choose an account to
+    // reset their password.
+    $this->drupalLogin($user_with_name);
+    $this->drupalGet('user/password');
+    // There should not be a form element for name.
+    $this->assertNoField('name', 'Duplicate user is not asked for a name when resetting password while logged in.');
+    $this->drupalPost(NULL, array(), t('E-mail new password'));
+    // Make sure the user with the matching username was sent an email.
+    $this->assertText(t('Further instructions have been sent to your e-mail address.'), 'User is notified that password reset was sent when logged in.');
+    $this->assertEqual(count($this->drupalGetMails(array('key' => 'password_reset', 'to' => $user_with_name->mail))), 1, 'The right user was sent a password reset mail when logged in.');
+    // Make sure that the user with the matching email address was not sent an
+    // email. (An email was already sent to this user earlier.)
+    $this->assertEqual(count($this->drupalGetMails(array('key' => 'password_reset', 'to' => $user_with_email->mail))), 1, 'The other user was not sent a password reset mail when logged in.');
+  }
+
+  /**
    * Tests password reset functionality.
    */
   function testUserPasswordReset() {
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
index 56ad9a0..b51d941 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserRegistrationTest.php
@@ -137,6 +137,43 @@ class UserRegistrationTest extends WebTestBase {
     $this->assertText(t('The e-mail address @email is already registered.', array('@email' => $duplicate_user->mail)), t('Supplying a duplicate email address with added whitespace displays an error message'));
   }
 
+  /**
+   * Ensure that a new account cannot be created when the username matches an
+   * existing user's email address, or when the email address matches an
+   * existing user's username.
+   */
+  function testRegistrationConflicts() {
+    // Don't require e-mail verification.
+    variable_set('user_email_verification', FALSE);
+
+    // Allow registration by site visitors without administrator approval.
+    variable_set('user_register', USER_REGISTER_VISITORS);
+
+    // Set up a user to check for duplicates.
+    $duplicate_user = $this->drupalCreateUser();
+
+    $edit = array();
+    $edit['name'] = $duplicate_user->mail;
+    $edit['mail'] = $this->randomName() . '@example.com';
+
+    // Attempt to create a new account using a username that matches an
+    // existing email.
+    $this->drupalPost('user/register', $edit, t('Create new account'));
+    $this->assertText(t('The name @name is already taken.', array('@name' => $edit['name'])), "A user cannot be created when their username matches an existing user's email address.");
+
+    // Change the username to an email address.
+    $duplicate_user->name = $name = $this->randomName() . '@example.com';
+    $duplicate_user->save();
+
+    $edit['name'] = $this->randomName();
+    $edit['mail'] = $name;
+
+    // Attempt to create a new account using an email that matches an existing
+    // username.
+    $this->drupalPost('user/register', $edit, t('Create new account'));
+    $this->assertText(t('The e-mail address @email is already registered.', array('@email' => $edit['mail'])), "A user cannot be created when their email address matches an existing username.");
+  }
+
   function testRegistrationDefaultValues() {
     // Allow registration by site visitors without administrator approval.
     variable_set('user_register', USER_REGISTER_VISITORS);