diff --git a/core/lib/Drupal/Core/Config/TypedConfigManager.php b/core/lib/Drupal/Core/Config/TypedConfigManager.php
index 24c118f..68c8511 100644
--- a/core/lib/Drupal/Core/Config/TypedConfigManager.php
+++ b/core/lib/Drupal/Core/Config/TypedConfigManager.php
@@ -190,6 +190,7 @@ protected function getDefinitionWithReplacements($base_plugin_id, array $replace
     $definition += array(
       'definition_class' => '\Drupal\Core\TypedData\DataDefinition',
       'type' => $type,
+      'unwrap_for_canonical_representation' => TRUE,
     );
     return $definition;
   }
diff --git a/core/lib/Drupal/Core/Validation/ConstraintManager.php b/core/lib/Drupal/Core/Validation/ConstraintManager.php
index 631a3d1..47d291a 100644
--- a/core/lib/Drupal/Core/Validation/ConstraintManager.php
+++ b/core/lib/Drupal/Core/Validation/ConstraintManager.php
@@ -12,6 +12,9 @@
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Plugin\DefaultPluginManager;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\Validator\Constraints\Choice;
+use Symfony\Component\Validator\Constraints\EqualTo;
+use Symfony\Component\Validator\Constraints\GreaterThan;
 
 /**
  * Constraint plugin manager.
diff --git a/core/modules/config/tests/config_test/config/install/config_test.validation.yml b/core/modules/config/tests/config_test/config/install/config_test.validation.yml
new file mode 100644
index 0000000..47b397d
--- /dev/null
+++ b/core/modules/config/tests/config_test/config/install/config_test.validation.yml
@@ -0,0 +1,7 @@
+llama: meh
+cat:
+  type: kitten
+  count: 2
+giraffe:
+  hum1: hum1
+  hum2: hum2
diff --git a/core/modules/config/tests/config_test/config/schema/config_test.schema.yml b/core/modules/config/tests/config_test/config/schema/config_test.schema.yml
index 6cad91b..91f4fd6 100644
--- a/core/modules/config/tests/config_test/config/schema/config_test.schema.yml
+++ b/core/modules/config/tests/config_test/config/schema/config_test.schema.yml
@@ -152,3 +152,30 @@ config_test.foo:
 
 config_test.bar:
   type: config_test.foo
+
+config_test.validation:
+  type: config_object
+  label: 'Configuration type'
+  mapping:
+    llama:
+      type: string
+      constraints:
+        Callback:
+          callback: [\Drupal\config_test\ConfigValidation, validateLlama]
+    cat:
+      type: mapping
+      mapping:
+        type:
+          type: string
+          constraints:
+            Callback:
+              callback: [\Drupal\config_test\ConfigValidation, validateCats]
+        count:
+          type: integer
+          constraints:
+            Callback:
+              callback: [\Drupal\config_test\ConfigValidation, validateCatCount]
+    giraffe:
+      type: sequence
+      sequence:
+        type: string
diff --git a/core/modules/config/tests/config_test/src/ConfigValidation.php b/core/modules/config/tests/config_test/src/ConfigValidation.php
new file mode 100644
index 0000000..9da6862
--- /dev/null
+++ b/core/modules/config/tests/config_test/src/ConfigValidation.php
@@ -0,0 +1,24 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\config_test\ConfigValidation.
+ */
+
+namespace Drupal\config_test;
+
+class ConfigValidation {
+
+  public static function validateLlama($object, $context) {
+    return $object === 'meh';
+  }
+
+  public static function validateCats($object, $context) {
+    return in_array($object, ['kitten', 'cats', 'nyans']);
+  }
+
+  public static function validateCatCount($object, $context) {
+    return $object > 1;
+  }
+
+}
diff --git a/core/tests/Drupal/KernelTests/Config/ConfigValidationTest.php b/core/tests/Drupal/KernelTests/Config/ConfigValidationTest.php
new file mode 100644
index 0000000..c9796dd
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Config/ConfigValidationTest.php
@@ -0,0 +1,67 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\KernelTests\Config\ConfigValidationTest.
+ */
+
+namespace Drupal\KernelTests\Config;
+use Drupal\KernelTests\KernelTestBase;
+use Symfony\Component\Validator\ConstraintViolationListInterface;
+
+/**
+ * Tests config validation mechanism
+ */
+class ConfigValidationTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['config_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installConfig('config_test');
+  }
+
+  public function testSimpleConfigValidation() {
+    $config = \Drupal::configFactory()->getEditable('config_test.validation');
+    /** @var \Drupal\Core\Config\TypedConfigManagerInterface $typed_config_manager */
+    $typed_config_manager = \Drupal::service('config.typed');
+    /** @var \Drupal\Core\Config\Schema\TypedConfigInterface $typed_config */
+    $typed_config = $typed_config_manager->get('config_test.validation');
+
+    $result = $typed_config->validate();
+    $this->assertInstanceOf(ConstraintViolationListInterface::class, $result);
+    $this->assertEmpty($result);
+
+    // Test constraints on primitive types.
+    $config->set('llama', 'muh');
+    $config->save();
+
+    $typed_config = $typed_config_manager->get('config_test.validation');
+    $result = $typed_config->validate();
+    // 1. llama is no longer a string and 2. its not meh anymore.
+    $this->assertCount(2, $result);
+
+    // Test constraints on mapping
+    $config->set('cat.type', 'nyans');
+    $config->save();
+
+    $typed_config = $typed_config_manager->get('config_test.validation');
+    $result = $typed_config->validate();
+    $this->assertEmpty($result);
+
+    $config->set('cat.type', 'miaus');
+    $config->save();
+
+    $typed_config = $typed_config_manager->get('config_test.validation');
+    $result = $typed_config->validate();
+    $this->assertCount(2, $result);
+  }
+
+}