diff --git a/core/lib/Drupal/Component/PhpStorage/FileStorage.php b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
index 71ff3f2..69f0f47 100644
--- a/core/lib/Drupal/Component/PhpStorage/FileStorage.php
+++ b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
@@ -52,15 +52,22 @@ public function load($name) {
    * Implements Drupal\Component\PhpStorage\PhpStorageInterface::save().
    */
   public function save($name, $code) {
+    // When running on a site with a large amount of traffic, there is the slim
+    // possibility that two requests could end up in this function at the same
+    // time. First, check to see if the file is being written to the real file
+    // system and not a virtual one. If so, obtain an exclusive lock so that
+    // the entire contents are written out before another process reads or
+    // tries to write to the file.
     $path = $this->getFullPath($name);
+    $flags = parse_url($path, PHP_URL_SCHEME) == 'file' ? LOCK_EX : 0;
     $directory = dirname($path);
     if ($this->ensureDirectory($directory)) {
       $htaccess_path =  $directory . '/.htaccess';
-      if (!file_exists($htaccess_path) && file_put_contents($htaccess_path, static::htaccessLines())) {
+      if (!file_exists($htaccess_path) && file_put_contents($htaccess_path, static::htaccessLines(), $flags)) {
         @chmod($htaccess_path, 0444);
       }
     }
-    return (bool) file_put_contents($path, $code);
+    return (bool) file_put_contents($path, $code, $flags);
   }
 
   /**
@@ -131,9 +138,10 @@ public static function htaccessLines($private = TRUE) {
    *   TRUE if the directory exists or has been created, FALSE otherwise.
    */
   protected function ensureDirectory($directory, $mode = 0777) {
+    $flags = parse_url($directory, PHP_URL_SCHEME) == 'file' ? LOCK_EX : 0;
     if ($this->createDirectory($directory, $mode)) {
       $htaccess_path =  $directory . '/.htaccess';
-      if (!file_exists($htaccess_path) && file_put_contents($htaccess_path, static::htaccessLines())) {
+      if (!file_exists($htaccess_path) && file_put_contents($htaccess_path, static::htaccessLines(), $flags)) {
         @chmod($htaccess_path, 0444);
       }
     }
@@ -167,8 +175,9 @@ protected function createDirectory($directory, $mode = 0777, $is_backwards_recur
     // because mkdir() obeys the umask of the current process.
     if (is_dir($parent = dirname($directory))) {
       // If the parent directory exists, then the backwards recursion must end,
-      // regardless of whether the subdirectory could be created.
-      if ($status = mkdir($directory)) {
+      // regardless of whether the subdirectory could be created.  Since the
+      // return value is being checked, call mkdir() with warnings suppressed.
+      if ($status = @mkdir($directory)) {
         // Only try to chmod() if the subdirectory could be created.
         $status = chmod($directory, $mode);
       }
diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 9225712..340257b 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -127,10 +127,20 @@ public function loadTemplate($name, $index = NULL) {
           $this->updateCompiledTemplate($cache_filename, $name);
         }
 
-        if (!$this->storage()->load($cache_filename)) {
+        // Load the file, double-check that the class now exists to prevent rare
+        // race conditions in the storage.
+        if (!$this->storage()->load($cache_filename) || !class_exists($cls)) {
           $this->updateCompiledTemplate($cache_filename, $name);
           $this->storage()->load($cache_filename);
         }
+
+        if (!class_exists($cls, FALSE)) {
+          // In some rare race conditions with concurrent requests, we might
+          // have failed to load the class. In that case, execute the code
+          // directly to make the class available.
+          $compiled_source = $this->compileSource($this->loader->getSource($name), $name);
+          eval('?' . '>' . $compiled_source);
+        }
       }
     }
 
diff --git a/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php b/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php
index f113ead..8fd0ebe 100644
--- a/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigEnvironmentTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Theme;
 
 use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Core\PhpStorage\PhpStorageFactory;
 use Drupal\Core\Site\Settings;
 use Drupal\simpletest\KernelTestBase;
 
@@ -44,6 +45,19 @@ public function testInlineTemplate() {
     );
     $this->assertEqual(drupal_render($element), 'test-with-context ' . SafeMarkup::checkPlain($unsafe_string));
 
+    // Simulate an invalid, existing file in the storage.
+    $name = 'maintenance-page.html.twig';
+    $cache_file = $environment->getCacheFilename($name);
+    $storage = PhpStorageFactory::get('twig');
+    $storage->save($cache_file, '<?php');
+
+    $element = array();
+    $element['test'] = array(
+      '#type' => 'inline_template',
+      '#template' => $name,
+    );
+    $this->assertEqual(drupal_render($element), $name);
+
     // Enable twig_auto_reload and twig_debug.
     $settings = Settings::getAll();
     $settings['twig_debug'] = TRUE;