diff --git a/core/lib/Drupal/Component/PhpStorage/FileStorage.php b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
index e4e7fde..a9f0759 100644
--- a/core/lib/Drupal/Component/PhpStorage/FileStorage.php
+++ b/core/lib/Drupal/Component/PhpStorage/FileStorage.php
@@ -20,6 +20,21 @@ class FileStorage implements PhpStorageInterface {
   protected $directory;
 
   /**
+   * Set to TRUE if this is a Windows server.
+   *
+   * @var bool
+   */
+  protected $is_windows;
+
+  /**
+   * Stores the Unicode-compatible verison of $directory for use on Windows
+   * servers with a 260 MAX_PATH limitation.
+   *
+   * @var string
+   */
+  protected $windows_path;
+
+  /**
    * Constructs this FileStorage object.
    *
    * @param array $configuration
@@ -29,10 +44,56 @@ class FileStorage implements PhpStorageInterface {
    *     the same configuration, but for different bins..
    */
   public function __construct(array $configuration) {
-    $this->directory = $configuration['directory'] . '/' . $configuration['bin'];
+    // We must use the appropriate directory separator since we're using the
+    // Unicode path on Windows.
+    $this->directory = $configuration['directory'] . DIRECTORY_SEPARATOR . $configuration['bin'];
+    $this->is_windows = strtoupper(substr(PHP_OS, 0, 3)) === 'WIN';
+    if ($this->is_windows) {
+      $this->windows_path = $this->convertToUnicodePath($this->directory);
+    }
   }
 
   /**
+   * Converts a standard path to a Windows-compatible Unicode path on the
+   * Windows platform, allowing Windows to use paths greater than 260
+   * characters. Does nothing to an already-converted path or any path on a
+   * non-Windows platform.
+   *
+   * @param string $path
+   *   The path to convert. Some part of $path must be an existing directory .
+   *
+   * @see https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
+   */
+  protected function convertToUnicodePath($path) {
+    if (!$this->is_windows || strpos($path, '\\\\?\\') !== FALSE) {
+      // If the path has already been converted, no need to do it again.
+      return $path;
+    }
+
+    // Relative paths are not allowed with the '\\?\' notation, so we use
+    // realpath() to resolve them. Since realpath() returns false if the file or
+    // directory does not exist, we walk up the specified directory until we
+    // find an existing directory and use realpath() to determine the full path,
+    // prepend the '\\?\' notation to it, and remove that part of the path from
+    // $directory.
+    $previous = '';
+    $parent = dirname($this->directory);
+    while (!($realpath = realpath($parent)) && $parent != $previous) {
+      $previous = $parent;
+      $parent = dirname($parent);
+    }
+    assert(!empty($realpath), 'Unable to find a Windows Unicode path for ' . $path);
+
+    // Replace the existing part of $directory with the realpath version
+    // prefixed by the '\\?\' notation.
+    $return = '\\\\?\\' . $realpath . str_replace($parent, '', $path);
+
+    // Cannot use forward-slashes in paths when using the '\\?\' syntax on
+    // Windows.
+    $return = str_replace('/', '\\', $return);
+    return $return;
+  }
+  /**
    * {@inheritdoc}
    */
   public function exists($name) {
@@ -55,12 +116,20 @@ public function save($name, $code) {
     $path = $this->getFullPath($name);
     $directory = dirname($path);
     if ($this->ensureDirectory($directory)) {
-      $htaccess_path =  $directory . '/.htaccess';
-      if (!file_exists($htaccess_path) && file_put_contents($htaccess_path, static::htaccessLines())) {
-        @chmod($htaccess_path, 0444);
+      if ($this->is_windows) {
+        // Cannot use file_put_contents with a Windows Unicode (prefixed
+        // with '\\?\') path. Instead we write to a temp file and move it to
+        // the final location.
+        $temp = \Drupal::service('file_system')->tempnam(file_directory_temp(), 'filestorage_');
+        if (file_put_contents($temp, $code)) {
+          return rename($temp, $path);
+        }
+      }
+      else {
+        return (bool) file_put_contents($path, $code);
       }
     }
-    return (bool) file_put_contents($path, $code);
+    return FALSE;
   }
 
   /**
@@ -114,7 +183,7 @@ public static function htaccessLines($private = TRUE) {
   }
 
   /**
-   * Ensures the directory exists, has the right permissions, and a .htaccess.
+   * Ensures the directory exists, has the right permissions and a .htaccess.
    *
    * For compatibility with open_basedir, the requested directory is created
    * using a recursion logic that is based on the relative directory path/tree:
@@ -131,12 +200,32 @@ public static function htaccessLines($private = TRUE) {
    *   TRUE if the directory exists or has been created, FALSE otherwise.
    */
   protected function ensureDirectory($directory, $mode = 0777) {
+    if ($this->is_windows) {
+      $directory = $this->convertToUnicodePath($directory);
+    }
     if ($this->createDirectory($directory, $mode)) {
-      $htaccess_path =  $directory . '/.htaccess';
-      if (!file_exists($htaccess_path) && file_put_contents($htaccess_path, static::htaccessLines())) {
-        @chmod($htaccess_path, 0444);
+      // We must use the appropriate directory separator since we're using the
+      // Unicode path on Windows.
+      $htaccess_path =  $directory . DIRECTORY_SEPARATOR . '.htaccess';
+      if (!file_exists($htaccess_path)) {
+        if ($this->is_windows) {
+          // Cannot use file_put_contents with a Windows Unicode (prefixed
+          // with '\\?\') path. Instead we write to a temp file and move it to
+          // the final location.
+          $temp = \Drupal::service('file_system')->tempnam(file_directory_temp(), 'filestorage_');
+          if (file_put_contents($temp, static::htaccessLines())) {
+            rename($temp, $htaccess_path);
+            return @chmod($htaccess_path, 0444);
+          }
+        }
+        else {
+          if (file_put_contents($htaccess_path, static::htaccessLines())) {
+            return @chmod($htaccess_path, 0444);
+          }
+        }
       }
     }
+    return FALSE;
   }
 
   /**
@@ -159,10 +248,17 @@ protected function ensureDirectory($directory, $mode = 0777) {
    *   TRUE if the directory exists or has been created, FALSE otherwise.
    */
   protected function createDirectory($directory, $mode = 0777, $is_backwards_recursive = FALSE) {
+    // createDirectory() can be called recursively. Only convert to the Windows
+    // path on the initial call, if needed.
+    if ($this->is_windows && !$is_backwards_recursive) {
+      $directory = $this->convertToUnicodePath($directory);
+    }
+
     // If the directory exists already, there's nothing to do.
     if (is_dir($directory)) {
       return TRUE;
     }
+
     // Otherwise, try to create the directory and ensure to set its permissions,
     // because mkdir() obeys the umask of the current process.
     if (is_dir($parent = dirname($directory))) {
@@ -197,7 +293,8 @@ public function delete($name) {
    * {@inheritdoc}
    */
   public function getFullPath($name) {
-    return $this->directory . '/' . $name;
+    $directory = $this->is_windows ? $this->windows_path : $this->directory;
+    return $directory . DIRECTORY_SEPARATOR . $name;
   }
 
   /**
@@ -211,7 +308,8 @@ public function writeable() {
    * {@inheritdoc}
    */
   public function deleteAll() {
-    return $this->unlink($this->directory);
+    $directory = $this->is_windows ? $this->windows_path : $this->directory;
+    return $this->unlink($directory);
   }
 
   /**
@@ -253,8 +351,9 @@ protected function unlink($path) {
    */
   public function listAll() {
     $names = array();
-    if (file_exists($this->directory)) {
-      foreach (new \DirectoryIterator($this->directory) as $fileinfo) {
+    $directory = $this->is_windows ? $this->windows_path : $this->directory;
+    if (file_exists($directory)) {
+      foreach (new \DirectoryIterator($directory) as $fileinfo) {
         if (!$fileinfo->isDot()) {
           $name = $fileinfo->getFilename();
           if ($name != '.htaccess') {