diff --git a/core/lib/Drupal/Core/Access/AccessException.php b/core/lib/Drupal/Core/Access/AccessException.php
new file mode 100644
index 0000000..a44738e
--- /dev/null
+++ b/core/lib/Drupal/Core/Access/AccessException.php
@@ -0,0 +1,14 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Access\AccessException.
+ */
+
+namespace Drupal\Core\Access;
+
+/**
+ * An exception thrown for invalid access callback return values.
+ */
+class AccessException extends \RuntimeException {
+}
diff --git a/core/lib/Drupal/Core/Access/AccessManager.php b/core/lib/Drupal/Core/Access/AccessManager.php
index 5959fd0..43f8cf1 100644
--- a/core/lib/Drupal/Core/Access/AccessManager.php
+++ b/core/lib/Drupal/Core/Access/AccessManager.php
@@ -259,6 +259,11 @@ protected function checkAll(array $checks, Route $route, Request $request) {
       }
 
       $service_access = $this->checks[$service_id]->access($route, $request);
+
+      if (!in_array($service_access, array(AccessInterface::ALLOW, AccessInterface::DENY, AccessInterface::KILL), TRUE)) {
+        throw new AccessException('Access services can only return AccessInterface::ALLOW, AccessInterface::DENY, or AccessInterface::KILL constants.');
+      }
+
       if ($service_access === AccessInterface::ALLOW) {
         $access = TRUE;
       }
@@ -295,6 +300,11 @@ protected function checkAny(array $checks, $route, $request) {
       }
 
       $service_access = $this->checks[$service_id]->access($route, $request);
+
+      if (!in_array($service_access, array(AccessInterface::ALLOW, AccessInterface::DENY, AccessInterface::KILL), TRUE)) {
+        throw new AccessException('Access services can only return AccessInterface::ALLOW, AccessInterface::DENY, or AccessInterface::KILL constants.');
+      }
+
       if ($service_access === AccessInterface::ALLOW) {
         $access = TRUE;
       }
diff --git a/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php b/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php
index d12f5c0..edfe7e0 100644
--- a/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Access/AccessManagerTest.php
@@ -461,6 +461,68 @@ public function testCheckNamedRouteWithNonExistingRoute() {
   }
 
   /**
+   * Tests that an access checker throws an exception for not allowed values.
+   *
+   * @dataProvider providerCheckException
+   *
+   * @expectedException \Drupal\Core\Access\AccessException
+   */
+  public function testCheckException($return_value, $access_mode) {
+    $this->routeProvider = $this->getMock('Drupal\Core\Routing\RouteProviderInterface');
+
+    // Setup a test route for each access configuration.
+    $requirements = array(
+      '_test_incorrect_value' => 'TRUE',
+    );
+    $options = array(
+      '_access_mode' => $access_mode,
+      '_access_checks' => array(
+        'test_incorrect_value',
+      ),
+    );
+    $route = new Route('', array(), $requirements, $options);
+
+    $this->routeProvider->expects($this->any())
+      ->method('getRouteByName')
+      ->will($this->returnValue($route));
+
+    $request = new Request();
+
+    // Register a service that will return an incorrect value.
+    $access_check = $this->getMock('Drupal\Core\Access\AccessInterface');
+    $access_check->expects($this->any())
+      ->method('access')
+      ->will($this->returnValue($return_value));
+    $this->container->register('test_incorrect_value', $access_check);
+
+    $this->accessManager = new AccessManager($this->routeProvider, $this->urlGenerator, $this->paramConverter);
+    $this->accessManager->setContainer($this->container);
+    $this->accessManager->addCheckService('test_incorrect_value');
+
+    $this->accessManager->checkNamedRoute('test_incorrect_value', array(), $request);
+  }
+
+  /**
+   * Data provider for testCheckException.
+   *
+   * @return array
+   */
+  public function providerCheckException() {
+    return array(
+      array(array(), 'ALL'),
+      array(array(), 'ANY'),
+      array(array(1), 'ALL'),
+      array(array(1), 'ANY'),
+      array('string', 'ALL'),
+      array('string', 'ANY'),
+      array(0, 'ALL'),
+      array(0, 'ANY'),
+      array(1, 'ALL'),
+      array(1, 'ANY'),
+    );
+  }
+
+  /**
    * Converts AccessCheckInterface constants to a string.
    *
    * @param mixed $constant