diff --git a/core/lib/Drupal/Core/Extension/ModuleHandler.php b/core/lib/Drupal/Core/Extension/ModuleHandler.php
index 95dd5a8..d02485a 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandler.php
@@ -1092,8 +1092,8 @@ public function getName($module) {
   /**
    * {@inheritdoc}
    */
-  public function invalidCore($core) {
-    return substr(\Drupal::CORE_COMPATIBILITY, 0, 1) != substr($core, 0, 1) || version_compare(\Drupal::VERSION, $core, '<');
+  public function isCoreCompatible($core) {
+    return substr(\Drupal::CORE_COMPATIBILITY, 0, 1) == substr($core, 0, 1) && !version_compare(\Drupal::VERSION, $core, '<');
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php b/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
index 15b07a5..6cd03f2 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandlerInterface.php
@@ -360,12 +360,12 @@ public function getName($theme);
   /**
    * Check a module's core compatibility
    *
-   * @param $core
+   * @param string $core
    *   The value of the core key in a module .info.yml file.
    *
    * @return bool
-   *   TRUE if invalid or incompatible, FALSE otherwise.
+   *   FALSE if invalid or incompatible, TRUE otherwise.
    */
-  public function invalidCore($core);
+  public function isCoreCompatible($core);
 
 }
diff --git a/core/modules/system/src/Controller/SystemController.php b/core/modules/system/src/Controller/SystemController.php
index 22bade6..d21674f 100644
--- a/core/modules/system/src/Controller/SystemController.php
+++ b/core/modules/system/src/Controller/SystemController.php
@@ -230,7 +230,7 @@ public function themesPage() {
         // Ensure this theme is compatible with this version of core.
         // Require the 'content' region to make sure the main page
         // content has a common place in all themes.
-        $theme->incompatible_core = !isset($theme->info['core']) || ($theme->info['core'] != \DRUPAL::CORE_COMPATIBILITY) || !isset($theme->info['regions']['content']);
+        $theme->incompatible_core = !isset($theme->info['core']) || !$this->moduleHandler()->isCoreCompatible($theme->info['core']) || !isset($theme->info['regions']['content']);
         $theme->incompatible_php = version_compare(phpversion(), $theme->info['php']) < 0;
         // Confirmed that the base theme is available.
         $theme->incompatible_base = isset($theme->info['base theme']) && !isset($themes[$theme->info['base theme']]);
diff --git a/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
index 2830a40..c458f92 100644
--- a/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -336,7 +336,7 @@ protected function buildRow(array $modules, Extension $module, $distribution) {
     $reasons = array();
 
     // Check the core compatibility.
-    if ($this->moduleHandler->invalidCore($module->info['core'])) {
+    if (!$this->moduleHandler->isCoreCompatible($module->info['core'])) {
       $compatible = FALSE;
       $reasons[] = $this->t('This version is not compatible with Drupal !core_version and should be replaced.', array(
         '!core_version' => \Drupal::VERSION,
@@ -381,7 +381,7 @@ protected function buildRow(array $modules, Extension $module, $distribution) {
         }
         // Disable the checkbox if the dependency is incompatible with this
         // version of Drupal core.
-        elseif ($this->moduleHandler->invalidCore($modules[$dependency]->info['core'])) {
+        elseif (!$this->moduleHandler->isCoreCompatible($modules[$dependency]->info['core'])) {
           $row['#requires'][$dependency] = $this->t('@module (<span class="admin-missing">incompatible with</span> this version of Drupal core)', array(
             '@module' => $name,
           ));
diff --git a/core/modules/system/tests/modules/system_test/system_test.module.orig b/core/modules/system/tests/modules/system_test/system_test.module.orig
deleted file mode 100644
index 8024680..0000000
--- a/core/modules/system/tests/modules/system_test/system_test.module.orig
+++ /dev/null
@@ -1,192 +0,0 @@
-<?php
-
-use Drupal\Core\Extension\Extension;
-use Symfony\Component\HttpFoundation\RedirectResponse;
-
-/**
- * Implements hook_modules_installed().
- */
-function system_test_modules_installed($modules) {
-  if (\Drupal::state()->get('system_test.verbose_module_hooks')) {
-    foreach ($modules as $module) {
-      drupal_set_message(t('hook_modules_installed fired for @module', array('@module' => $module)));
-    }
-  }
-}
-
-/**
- * Implements hook_modules_uninstalled().
- */
-function system_test_modules_uninstalled($modules) {
-  if (\Drupal::state()->get('system_test.verbose_module_hooks')) {
-    foreach ($modules as $module) {
-      drupal_set_message(t('hook_modules_uninstalled fired for @module', array('@module' => $module)));
-    }
-  }
-}
-
-/**
- * Implements hook_system_info_alter().
- */
-function system_test_system_info_alter(&$info, Extension $file, $type) {
-  // We need a static otherwise the last test will fail to alter common_test.
-  static $test;
-  if (($dependencies = \Drupal::state()->get('system_test.dependencies')) || $test) {
-    if ($file->getName() == 'module_test') {
-      $info['hidden'] = FALSE;
-      $info['dependencies'][] = array_shift($dependencies);
-      \Drupal::state()->set('system_test.dependencies', $dependencies);
-      $test = TRUE;
-    }
-    if ($file->getName() == 'common_test') {
-      $info['hidden'] = FALSE;
-      $info['version'] = '8.x-2.4-beta3';
-    }
-  }
-
-  // Make the system_dependencies_test visible by default.
-  if ($file->getName() == 'system_dependencies_test') {
-    $info['hidden'] = FALSE;
-  }
-  if (in_array($file->getName(), array(
-    'system_incompatible_module_version_dependencies_test',
-    'system_incompatible_core_version_dependencies_test',
-    'system_incompatible_module_version_test',
-    'system_incompatible_core_version_test',
-  ))) {
-    $info['hidden'] = FALSE;
-  }
-  if ($file->getName() == 'requirements1_test' || $file->getName() == 'requirements2_test') {
-    $info['hidden'] = FALSE;
-  }
-  if ($file->getName() == 'system_test') {
-    $info['hidden'] = \Drupal::state()->get('system_test.module_hidden', TRUE);
-  }
-}
-
-/**
- * Try to acquire a named lock and report the outcome.
- *
- * @deprecated \Drupal\system_test\Controller\SystemTestController::lockAcquire()
- */
-function system_test_lock_acquire() {
-  if (\Drupal::lock()->acquire('system_test_lock_acquire')) {
-    \Drupal::lock()->release('system_test_lock_acquire');
-    return ['#markup' => 'TRUE: Lock successfully acquired in system_test_lock_acquire()'];
-  }
-  else {
-    return ['#markup' => 'FALSE: Lock not acquired in system_test_lock_acquire()'];
-  }
-}
-
-/**
- * Try to acquire a specific lock, and then exit.
- *
- * @deprecated \Drupal\system_test\Controller\SystemTestController::lockExit()
- */
-function system_test_lock_exit() {
-  if (\Drupal::lock()->acquire('system_test_lock_exit', 900)) {
-    echo 'TRUE: Lock successfully acquired in system_test_lock_exit()';
-    // The shut-down function should release the lock.
-    exit();
-  }
-  else {
-    return ['#markup' => 'FALSE: Lock not acquired in system_test_lock_exit()'];
-  }
-}
-
-/**
- * Implements hook_page_attachments().
- */
-function system_test_page_attachments(array &$page) {
-  $menu_item['path'] = current_path();
-  $main_content_display = &drupal_static('system_main_content_added', FALSE);
-
-  if ($menu_item['path'] == 'system-test/main-content-fallback') {
-    // Get the main content, to e.g. dynamically attach an asset.
-    drupal_set_page_content();
-    // Indicate we don't want to override the main content.
-    $main_content_display = FALSE;
-  }
-  elseif ($menu_item['path'] == 'system-test/main-content-handling') {
-    // Set the main content.
-    drupal_set_page_content('<div id="system-test-content">Overridden!</div>');
-  }
-  // Used by FrontPageTestCase to get the results of drupal_is_front_page().
-  $frontpage = \Drupal::state()->get('system_test.front_page_output') ?: 0;
-  if ($frontpage && drupal_is_front_page()) {
-    drupal_set_message(t('On front page.'));
-  }
-}
-
-/**
- * A simple page callback which adds a register shutdown function.
- *
- * @deprecated \Drupal\system_test\Controller\SystemTestController::shutdownFunctions()
- */
-function system_test_page_shutdown_functions($arg1, $arg2) {
-  drupal_register_shutdown_function('_system_test_first_shutdown_function', $arg1, $arg2);
-}
-
-/**
- * Dummy shutdown function which registers another shutdown function.
- */
-function _system_test_first_shutdown_function($arg1, $arg2) {
-  // Set something to ensure that this function got called.
-  \Drupal::state()->set('_system_test_first_shutdown_function', array($arg1, $arg2));
-  drupal_register_shutdown_function('_system_test_second_shutdown_function', $arg1, $arg2);
-}
-
-/**
- * Dummy shutdown function.
- */
-function _system_test_second_shutdown_function($arg1, $arg2) {
-  // Set something to ensure that this function got called.
-  \Drupal::state()->set('_system_test_second_shutdown_function', array($arg1, $arg2));
-
-  // Throw an exception with an HTML tag. Since this is called in a shutdown
-  // function, it will not bubble up to the default exception handler but will
-  // be caught in _drupal_shutdown_function() and be displayed through
-  // \Drupal\Core\Utility\Error::renderExceptionSafe() if possible.
-  throw new Exception('Drupal is <blink>awesome</blink>.');
-}
-
-/**
- * Implements hook_filetransfer_info().
- */
-function system_test_filetransfer_info() {
-  return array(
-    'system_test' => array(
-      'title' => t('System Test FileTransfer'),
-      'class' => 'Drupal\system_test\MockFileTransfer',
-      'weight' => -10,
-    ),
-  );
-}
-
-/**
- * Page callback to initialize authorize.php during testing.
- *
- * @see system_authorized_init().
- *
- * @deprecated \Drupal\system_test\Controller\SystemTestController::authorizeInit()
- */
-function system_test_authorize_init_page($page_title) {
-  $authorize_url = $GLOBALS['base_url'] . '/core/authorize.php';
-  system_authorized_init('system_test_authorize_run', drupal_get_path('module', 'system_test') . '/system_test.module', array(), $page_title);
-  return new RedirectResponse($authorize_url);
-}
-
-/**
- * Implements hook_module_preinstall().
- */
-function system_test_module_preinstall($module) {
-  \Drupal::state()->set('system_test_preinstall_module', $module);
-}
-
-/**
- * Implements hook_module_preuninstall().
- */
-function system_test_module_preuninstall($module) {
-  \Drupal::state()->set('system_test_preuninstall_module', $module);
-}
diff --git a/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php b/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php
index 620e37d..7695646 100644
--- a/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php
+++ b/core/tests/Drupal/Tests/Core/Extension/ModuleHandlerTest.php
@@ -10,6 +10,7 @@
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ModuleHandler;
 use Drupal\Tests\UnitTestCase;
+use Symfony\Component\Validator\Constraints\False;
 
 /**
  * @coversDefaultClass \Drupal\Core\Extension\ModuleHandler
@@ -516,11 +517,11 @@ public function testGetModuleDirectories() {
   }
 
   /**
-   * @dataProvider providerInvalidCore
-   * @covers ::invalidCore
+   * @dataProvider providerIsCoreCompatible
+   * @covers ::isCoreCompatible
    */
-  public function testInvalidCore($version, $incompatible) {
-    $this->assertEquals($this->moduleHandler->invalidCore($version), $incompatible);
+  public function testIsCoreCompatible($version, $compatible) {
+    $this->assertEquals($compatible, $this->moduleHandler->isCoreCompatible($version));
   }
 
   /**
@@ -529,7 +530,7 @@ public function testInvalidCore($version, $incompatible) {
    * @return array
    *   An array of versions and whether they should be valid.
    */
-  public function providerInvalidCore() {
+  public function providerIsCoreCompatible() {
     $current = \Drupal::VERSION;
     list($major, $minor) = explode('.', $current);
 
@@ -538,16 +539,16 @@ public function providerInvalidCore() {
     $newer = $major + 1;
     $newer_minor = $major . '.' . ($minor + 1);
 
-    // Core version => invalid.
+    // Core version => valid.
     $versions = array(
       // Invalid.
-      "{$older}.x" => TRUE,
-      "{$older}.24" => TRUE,
-      "{$newer_minor}.x" => TRUE,
-      "{$newer}.0.x" => TRUE,
+      array("{$older}.x", FALSE),
+      array("{$older}.24", FALSE),
+      array("{$newer_minor}.x", FALSE),
+      array("{$newer}.0.x", FALSE),
       // Valid.
-      "{$major}.x" => FALSE,
-      "{$major}.{$minor}.x" => FALSE,
+      array("{$major}.x", TRUE),
+      array("{$major}.{$minor}.x", TRUE),
     );
 
     return $versions;