diff --git a/core/lib/Drupal/Core/Config/ConfigImporter.php b/core/lib/Drupal/Core/Config/ConfigImporter.php
index 66f51e4..dd5b9bb 100644
--- a/core/lib/Drupal/Core/Config/ConfigImporter.php
+++ b/core/lib/Drupal/Core/Config/ConfigImporter.php
@@ -263,6 +263,9 @@ public function import() {
    */
   public function validate() {
     if (!$this->validated) {
+      if (!$this->storageComparer->validateSiteUuid()) {
+        throw new ConfigImporterException('Site UUID in source storage does not match the target storage.');
+      }
       $this->notify('validate');
       $this->validated = TRUE;
     }
diff --git a/core/lib/Drupal/Core/Config/StorageComparer.php b/core/lib/Drupal/Core/Config/StorageComparer.php
index 834f439..c08cb5a 100644
--- a/core/lib/Drupal/Core/Config/StorageComparer.php
+++ b/core/lib/Drupal/Core/Config/StorageComparer.php
@@ -195,4 +195,13 @@ protected function getTargetNames() {
     return $this->targetNames;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function validateSiteUuid() {
+    $source = $this->sourceStorage->read('system.site');
+    $target = $this->targetStorage->read('system.site');
+    return $source['uuid'] === $target['uuid'];
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Config/StorageComparerInterface.php b/core/lib/Drupal/Core/Config/StorageComparerInterface.php
index 5ca0f3e..0f62d0c 100644
--- a/core/lib/Drupal/Core/Config/StorageComparerInterface.php
+++ b/core/lib/Drupal/Core/Config/StorageComparerInterface.php
@@ -117,4 +117,12 @@ public function reset();
    */
   public function hasChanges($ops = array('delete', 'create', 'update'));
 
+  /**
+   * Validates that the system.site::uuid in the source and target match.
+   *
+   * @return bool
+   *   TRUE if identical, FALSE if not.
+   */
+  public function validateSiteUuid();
+
 }
diff --git a/core/modules/config/lib/Drupal/config/Form/ConfigSync.php b/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
index 2994283..8e95d7e 100644
--- a/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
+++ b/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
@@ -160,6 +160,11 @@ public function buildForm(array $form, array &$form_state) {
       $form['actions']['#access'] = FALSE;
       return $form;
     }
+    elseif (!$storage_comparer->validateSiteUuid()) {
+      drupal_set_message($this->t('The staged configuration cannot be imported, because it originates from a different site than this site. You can only synchronize configuration between cloned instances of this site.'), 'error');
+      $form['actions']['#access'] = FALSE;
+      return $form;
+    }
     else {
       // Store the comparer for use in the submit.
       $form_state['storage_comparer'] = $storage_comparer;
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php
index 539879a..a214b63 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php
@@ -21,6 +21,13 @@
 class ConfigExportImportUITest extends WebTestBase {
 
   /**
+   * The site UUID.
+   *
+   * @var string
+   */
+  protected $siteUuid;
+
+  /**
    * The slogan value, for a simple export test case.
    *
    * @var string
@@ -69,6 +76,8 @@ protected function setUp() {
    * Tests a simple site configuration export case: site slogan.
    */
   function testExport() {
+    $this->siteUuid = \Drupal::config('system.site')->get('uuid');
+
     // Create a role for second round.
     $this->admin_role = $this->drupalCreateRole(array('synchronize configuration', 'import configuration'));
     $this->slogan = $this->randomString(16);
@@ -104,6 +113,9 @@ function testImport() {
    *   The name of the tarball containing the configuration to be imported.
    */
   protected function doImport($filename) {
+    // The site UUIDs must match for the import to work.
+    \Drupal::config('system.site')->set('uuid', $this->siteUuid)->save();
+
     $this->assertNotEqual($this->slogan, \Drupal::config('system.site')->get('slogan'));
     $this->drupalPostForm('admin/config/development/configuration/full/import', array('files[import_tarball]' => $filename), 'Upload');
     $this->drupalPostForm(NULL, array(), 'Import all');
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php
index 2f4ac16..e495602 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigImportUITest.php
@@ -116,6 +116,23 @@ function testImportLock() {
   }
 
   /**
+   * Tests verification of site UUID before importing configuration.
+   */
+  function testImportSiteUuidValidation() {
+    $staging = \Drupal::service('config.storage.staging');
+    // Create updated configuration object.
+    $config_data = \Drupal::config('system.site')->get();
+    // Generate a new site UUID.
+    $config_data['uuid'] = \Drupal::service('uuid')->generate();
+    $staging->write('system.site', $config_data);
+
+    // Verify that there are configuration differences to import.
+    $this->drupalGet('admin/config/development/configuration');
+    $this->assertText(t('The staged configuration cannot be imported, because it originates from a different site than this site. You can only synchronize configuration between cloned instances of this site.'));
+    $this->assertNoFieldById('edit-submit', t('Import all'));
+  }
+
+  /**
    * Tests the screen that shows differences between active and staging.
    */
   function testImportDiff() {
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php
index 59ea550..6af6295 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigImporterTest.php
@@ -97,6 +97,25 @@ function testEmptyImportFails() {
   }
 
   /**
+   * Tests verification of site UUID before importing configuration.
+   */
+  function testSiteUuidValidate() {
+    $staging = \Drupal::service('config.storage.staging');
+    // Create updated configuration object.
+    $config_data = \Drupal::config('system.site')->get();
+    // Generate a new site UUID.
+    $config_data['uuid'] = \Drupal::service('uuid')->generate();
+    $staging->write('system.site', $config_data);
+    try {
+      $this->configImporter->reset()->import();
+      $this->assertFalse(FALSE, 'ConfigImporterException not thrown, invalid import was not stopped due to mis-matching site UUID.');
+    }
+    catch (ConfigImporterException $e) {
+      $this->assertEqual($e->getMessage(), 'Site UUID in source storage does not match the target storage.');
+    }
+  }
+
+  /**
    * Tests deletion of configuration during import.
    */
   function testDeleted() {
diff --git a/core/modules/system/config/schema/system.schema.yml b/core/modules/system/config/schema/system.schema.yml
index 0dabf5e..9d585f0 100644
--- a/core/modules/system/config/schema/system.schema.yml
+++ b/core/modules/system/config/schema/system.schema.yml
@@ -4,6 +4,9 @@ system.site:
   type: mapping
   label: 'Site information'
   mapping:
+    uuid:
+      type: string
+      label: 'Site UUID'
     name:
       type: label
       label: 'Site name'
diff --git a/core/modules/system/config/system.site.yml b/core/modules/system/config/system.site.yml
index b1c5df5..4be7ae6 100644
--- a/core/modules/system/config/system.site.yml
+++ b/core/modules/system/config/system.site.yml
@@ -1,3 +1,4 @@
+uuid: ''
 name: Drupal
 mail: ''
 slogan: ''
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 14153a0..34d8dde 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -565,6 +565,11 @@ function system_install() {
   // Populate the cron key state variable.
   $cron_key = Crypt::randomStringHashed(55);
   \Drupal::state()->set('system.cron_key', $cron_key);
+
+  // Populate the site UUID.
+  \Drupal::config('system.site')
+    ->set('uuid', \Drupal::service('uuid')->generate())
+    ->save();
 }
 
 /**