diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountryConstraint.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountryConstraint.php
new file mode 100644
index 0000000..11f1455
--- /dev/null
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountryConstraint.php
@@ -0,0 +1,24 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Validation\Plugin\Validation\Constraint\CountryConstraint.
+ */
+
+namespace Drupal\Core\Validation\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Country constraint.
+ *
+ * @Plugin(
+ *   id = "Country",
+ *   label = @Translation("Country", context = "Validation")
+ * )
+ */
+class CountryConstraint extends Constraint {
+
+  public $message = 'This value is not a valid country.';
+
+}
diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountryConstraintValidator.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountryConstraintValidator.php
new file mode 100644
index 0000000..87ed795
--- /dev/null
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/CountryConstraintValidator.php
@@ -0,0 +1,64 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Validation\Plugin\Validation\Constraint\CountryConstraintValidator.
+ */
+
+namespace Drupal\Core\Validation\Plugin\Validation\Constraint;
+
+use Drupal\Core\Locale\CountryManagerInterface;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedTypeException;
+
+/**
+ * Validates the country code.
+ */
+class CountryConstraintValidator extends ConstraintValidator
+{
+  /**
+   * The country manager.
+   *
+   * @var \Drupal\Core\Locale\CountryManagerInterface
+   */
+  protected $countryManager;
+
+  /**
+   * Constructs a new CountryConstraintValidator.
+   *
+   * @param \Drupal\Core\Locale\CountryManagerInterface $country_manager
+   *   The country manager.
+   */
+  public function __construct(CountryManagerInterface $country_manager) {
+    $this->countryManager = $country_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static($container->get('country_manager'));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($value, Constraint $constraint) {
+    if ($value === null || $value === '') {
+      return;
+    }
+
+    if (!is_scalar($value) && !(is_object($value) && method_exists($value, '__toString'))) {
+      throw new UnexpectedTypeException($value, 'string');
+    }
+
+    $countries = $this->countryManager->getList();
+    $value = (string) $value;
+
+    if (!isset($countries[$value])) {
+      $this->context->addViolation($constraint->message);
+    }
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/CountryConstraintValidatorTest.php b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/CountryConstraintValidatorTest.php
new file mode 100644
index 0000000..273171a
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/CountryConstraintValidatorTest.php
@@ -0,0 +1,59 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Validation\Plugin\Validation\Constraint\CountryConstraintValidatorTest.
+ */
+
+namespace Drupal\Tests\Core\Validation\Plugin\Validation\Constraint;
+
+use Drupal\Core\TypedData\PrimitiveInterface;
+use Drupal\Core\Validation\Plugin\Validation\Constraint\CountryConstraint;
+use Drupal\Core\Validation\Plugin\Validation\Constraint\CountryConstraintValidator;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass Drupal\Core\Validation\Plugin\Validation\Constraint\CountryConstraintValidator
+ * @group validation
+ */
+class CountryConstraintValidatorTest extends UnitTestCase {
+
+  /**
+   * @covers ::validate
+   *
+   * @dataProvider provideTestValidate
+   */
+  public function testValidate($value, $valid) {
+    $country_manager = $this->getMock('Drupal\Core\Locale\CountryManagerInterface');
+    $country_manager->expects($this->any())
+      ->method('getList')
+      ->willReturn(['FR' => 'France', 'RS' => 'Serbia']);
+    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    if ($valid) {
+      $context->expects($this->never())
+        ->method('addViolation');
+    }
+    else {
+      $context->expects($this->once())
+        ->method('addViolation');
+    }
+
+    $constraint = new CountryConstraint();
+    $validate = new CountryConstraintValidator($country_manager);
+    $validate->initialize($context);
+    $validate->validate($value, $constraint);
+  }
+
+  public function provideTestValidate() {
+    return [
+      [NULL, TRUE],
+      ['', TRUE],
+      ['FR', TRUE],
+      ['RS', TRUE],
+      ['INVALID', FALSE],
+    ];
+
+    return $data;
+  }
+
+}