diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/UniqueFieldValueValidator.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/UniqueFieldValueValidator.php
index 7f51054..6fbf559 100644
--- a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/UniqueFieldValueValidator.php
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/UniqueFieldValueValidator.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Validation\Plugin\Validation\Constraint;
 
+use Drupal\Component\Utility\Unicode;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidator;
 
@@ -40,7 +41,7 @@ public function validate($items, Constraint $constraint) {
       $this->context->addViolation($constraint->message, [
         '%value' => $item->value,
         '%entity_type' => $entity->getEntityType()->getLowercaseLabel(),
-        '%field_name' => $items->getFieldDefinition()->getLabel(),
+        '%field_name' => Unicode::strtolower($items->getFieldDefinition()->getLabel()),
       ]);
     }
   }
diff --git a/core/modules/user/src/Tests/UserEditTest.php b/core/modules/user/src/Tests/UserEditTest.php
index 46502f4..8883381 100644
--- a/core/modules/user/src/Tests/UserEditTest.php
+++ b/core/modules/user/src/Tests/UserEditTest.php
@@ -28,7 +28,7 @@ function testUserEdit() {
     // Test that error message appears when attempting to use a non-unique user name.
     $edit['name'] = $user2->getUsername();
     $this->drupalPostForm("user/" . $user1->id() . "/edit", $edit, t('Save'));
-    $this->assertRaw(t('The username %name is already taken.', array('%name' => $edit['name'])));
+    $this->assertRaw(t('The user with the name %name already exists.', array('%name' => $edit['name'])));
 
     // Check that filling out a single password field does not validate.
     $edit = array();
diff --git a/core/modules/user/src/Tests/UserRegistrationTest.php b/core/modules/user/src/Tests/UserRegistrationTest.php
index ff3fa30..e7ee6f3 100644
--- a/core/modules/user/src/Tests/UserRegistrationTest.php
+++ b/core/modules/user/src/Tests/UserRegistrationTest.php
@@ -141,13 +141,13 @@ function testRegistrationEmailDuplicates() {
 
     // Attempt to create a new account using an existing email address.
     $this->drupalPostForm('user/register', $edit, t('Create new account'));
-    $this->assertText(t('The email address @email is already taken.', array('@email' => $duplicate_user->getEmail())), 'Supplying an exact duplicate email address displays an error message');
+    $this->assertText(t('The user with the email @email already exists.', array('@email' => $duplicate_user->getEmail())), 'Supplying an exact duplicate email address displays an error message');
 
     // Attempt to bypass duplicate email registration validation by adding spaces.
     $edit['mail'] = '   ' . $duplicate_user->getEmail() . '   ';
 
     $this->drupalPostForm('user/register', $edit, t('Create new account'));
-    $this->assertText(t('The email address @email is already taken.', array('@email' => $duplicate_user->getEmail())), 'Supplying a duplicate email address with added whitespace displays an error message');
+    $this->assertText(t('The user with the email @email already exists.', array('@email' => $duplicate_user->getEmail())), 'Supplying a duplicate email address with added whitespace displays an error message');
   }
 
   function testRegistrationDefaultValues() {
diff --git a/core/modules/user/src/Tests/UserValidationTest.php b/core/modules/user/src/Tests/UserValidationTest.php
index ec44a79..c6512f1 100644
--- a/core/modules/user/src/Tests/UserValidationTest.php
+++ b/core/modules/user/src/Tests/UserValidationTest.php
@@ -102,7 +102,7 @@ function testValidation() {
     $violations = $user->validate();
     $this->assertEqual(count($violations), 1, 'Violation found on name collision.');
     $this->assertEqual($violations[0]->getPropertyPath(), 'name');
-    $this->assertEqual($violations[0]->getMessage(), t('The username %name is already taken.', array('%name' => 'existing')));
+    $this->assertEqual($violations[0]->getMessage(), t('The user with the name %name already exists.', array('%name' => 'existing')));
 
     // Make the name valid.
     $user->set('name', $this->randomMachineName());
@@ -131,7 +131,7 @@ function testValidation() {
     $violations = $user->validate();
     $this->assertEqual(count($violations), 1, 'Violation found when email already exists.');
     $this->assertEqual($violations[0]->getPropertyPath(), 'mail');
-    $this->assertEqual($violations[0]->getMessage(), t('The email address %mail is already taken.', array('%mail' => 'existing@example.com')));
+    $this->assertEqual($violations[0]->getMessage(), t('The user with the email %mail already exists.', array('%mail' => 'existing@example.com')));
     $user->set('mail', NULL);
     $violations = $user->validate();
     $this->assertEqual(count($violations), 1, 'E-mail addresses may not be removed');