diff --git a/core/modules/path/lib/Drupal/path/Tests/PathAliasTest.php b/core/modules/path/lib/Drupal/path/Tests/PathAliasTest.php
index dbd2f41..9e0066c 100644
--- a/core/modules/path/lib/Drupal/path/Tests/PathAliasTest.php
+++ b/core/modules/path/lib/Drupal/path/Tests/PathAliasTest.php
@@ -31,7 +31,7 @@ function setUp() {
     parent::setUp();
 
     // Create test user and login.
-    $web_user = $this->drupalCreateUser(array('create page content', 'edit own page content', 'administer url aliases', 'create url aliases'));
+    $web_user = $this->drupalCreateUser(array('create page content', 'edit own page content', 'administer url aliases', 'create url aliases', 'override url aliases'));
     $this->drupalLogin($web_user);
   }
 
@@ -219,4 +219,25 @@ function testDuplicateNodeAlias() {
     $this->assertText(t('The alias is already in use.'));
     $this->assertFieldByXPath("//input[@name='path[alias]' and contains(@class, 'error')]", $edit['path[alias]'], 'Textfield exists and has the error class.');
   }
+  
+  /**
+   * Tests that only valid aliases pass path_alias_is_override().
+   */
+  function testPathAliasIsOverride() {
+    $tests = array(
+      'admin' => TRUE,
+      '/Admin/content/' => TRUE,
+      'node/10000/edit' => TRUE,
+      'User' => TRUE,
+      'user/login' => TRUE,
+      'users_are_people_too' => FALSE,
+      'dries-sings-the-drupal-song' => FALSE,
+    );
+		
+    foreach ($tests AS $alias => $expected) {
+      // Test the override functionality itself.
+      $result = path_alias_is_override($alias);
+      $this->assertIdentical($expected, $result);
+    }
+  }
 }
diff --git a/core/modules/path/path.module b/core/modules/path/path.module
index 03be41b..e9969bd 100644
--- a/core/modules/path/path.module
+++ b/core/modules/path/path.module
@@ -49,6 +49,9 @@ function path_permission() {
     'create url aliases' => array(
       'title' => t('Create and edit URL aliases'),
     ),
+    'override url aliases' => array(
+      'title' => t('Override system aliases'),
+    ),
   );
 }
 
@@ -163,24 +166,61 @@ function path_form_element_validate($element, &$form_state, $complete_form) {
       form_set_value($element['langcode'], $form_state['values']['langcode'], $form_state);
     }
 
-    $path = $form_state['values']['path'];
+    // If the alias has not changed since the last time it was changed,
+    // it should still be valid.
+    if ($element['alias']['#default_value'] != $alias) {
+      $path = $form_state['values']['path'];
 
-    // Ensure that the submitted alias does not exist yet.
-    $query = db_select('url_alias')
-      ->condition('alias', $path['alias'])
-      ->condition('langcode', $path['langcode']);
-    if (!empty($path['source'])) {
-      $query->condition('source', $path['source'], '<>');
-    }
-    $query->addExpression('1');
-    $query->range(0, 1);
-    if ($query->execute()->fetchField()) {
-      form_error($element, t('The alias is already in use.'));
+      // Ensure that the submitted alias does not exist yet.
+      $query = db_select('url_alias')
+        ->condition('alias', $path['alias'])
+        ->condition('langcode', $path['langcode']);
+      if (!empty($path['source'])) {
+        $query->condition('source', $path['source'], '<>');
+      }
+      $query->addExpression('1');
+      $query->range(0, 1);
+      if ($query->execute()->fetchField()) {
+        form_error($element, t('The alias is already in use.'));
+      } elseif (path_alias_is_override($path['alias']) && !user_access('override url aliases')) {
+        form_error($element, t('The alias overrides an existing URL.'));
+      }
     }
   }
 }
 
 /**
+ * Validates that a path alias is valid.
+ *
+ * @param $alias
+ *   A string containing the alias in question.
+ *
+ * @return
+ *   TRUE if the alias overrides an existing path, FALSE otherwise.
+ */
+function path_alias_is_override($alias) {
+  $alias = strtolower(trim($alias, '/ '));
+
+  // We could create an alias that would conflict with another node/user/taxonomy
+  // later on, so we need to take account of that. (e.g. Create node 7
+  // with the alias 'node/9/delete'. It will make it impossible to delete
+  // node 9 later on without modifying node 7 first.)
+  $parts = explode('/', $alias, 2);
+  $restricted_paths = array('node', 'taxonomy', 'user');
+  if (in_array($parts[0], $restricted_paths)) {
+    return TRUE;
+  }
+
+  // Verify that no other module has reserved this address
+  $router_item = menu_get_item($alias);
+  if (!empty($router_item)) {
+    return TRUE;
+  }
+
+  return FALSE;
+}
+
+/**
  * Implements hook_node_insert().
  */
 function path_node_insert(EntityInterface $node) {