diff --git a/imagecache_external.api.php b/imagecache_external.api.php
index 904d210..c9ba491 100644
--- a/imagecache_external.api.php
+++ b/imagecache_external.api.php
@@ -12,7 +12,7 @@
  */
 function hook_imagecache_external_needs_refresh_alter(&$needs_refresh, $filepath) {
   // Example: refresh images at least once a week.
-  if (filemtime($filepath) > REQUEST_TIME - 60 * 60 * 24 * 7) {
+  if (filemtime($filepath) > \Drupal::time()->getRequestTime() - 60 * 60 * 24 * 7) {
     $needs_refresh = TRUE;
   }
 }
diff --git a/imagecache_external.module b/imagecache_external.module
index 64774fe..2d85a56 100755
--- a/imagecache_external.module
+++ b/imagecache_external.module
@@ -1,4 +1,5 @@
 <?php
+use Drupal\Core\File\FileSystemInterface;
 /**
  * @file
  * Allows the usage of Image Styles on external images.
@@ -109,7 +110,7 @@ function imagecache_external_generate_path($url) {
 
   // Check if this is a non-standard file stream and adjust accordingly.
   $scheme = $file_system->uriScheme($url);
-  $default_scheme = file_default_scheme();
+  $default_scheme = \Drupal::config('system.file')->get('default_scheme');
 
   if ($scheme == $default_scheme) {
     // Don't try fetch already existing files on local file system.
@@ -135,7 +136,7 @@ function imagecache_external_generate_path($url) {
   }
 
   $directory = $default_scheme . '://' . $config->get('imagecache_directory');
-  if (file_prepare_directory($directory, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS)) {
+  if (\Drupal::service('file_system')->prepareDirectory($directory, FileSystemInterface::CREATE_DIRECTORY | FileSystemInterface::MODIFY_PERMISSIONS)) {
     $needs_refresh = FALSE;
     $filepath = $directory . '/' . $filename;
     // Allow modules to add custom logic to check if it needs to be re-fetched.
@@ -211,10 +212,10 @@ function imagecache_external_fetch($url, $cachepath) {
     }
     if (!empty($result->getBody()) && $code != 400 && $code != 500 && $content_type_allowed) {
       if ($config->get('imagecache_external_management') == 'unmanaged') {
-        return file_unmanaged_save_data($result->getBody(), $cachepath, FILE_EXISTS_REPLACE);
+        return \Drupal::service('file_system')->saveData($result->getBody(), $cachepath, FileSystemInterface::EXISTS_REPLACE);
       }
       else {
-        $file = file_save_data($result->getBody(), $cachepath, FILE_EXISTS_REPLACE);
+        $file = file_save_data($result->getBody(), $cachepath, FileSystemInterface::EXISTS_REPLACE);
         return $file->getFileUri();
       }
     }
@@ -316,7 +317,7 @@ function imagecache_external_file_download($uri) {
  */
 function imagecache_external_get_directory_path() {
   $config = imagecache_external_config();
-  $scheme = file_default_scheme();
+  $scheme = \Drupal::config('system.file')->get('default_scheme');
   $wrapper = \Drupal::service('stream_wrapper_manager')->getViaScheme($scheme);
   $path = realpath($wrapper->getDirectoryPath() . '/' . $config->get('imagecache_directory'));
   return $path;
diff --git a/src/Form/SettingsForm.php b/src/Form/SettingsForm.php
index 1bb900d..1214fd6 100644
--- a/src/Form/SettingsForm.php
+++ b/src/Form/SettingsForm.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\imagecache_external\Form;
 
+use Drupal\Core\File\FileSystemInterface;
 use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Form\FormStateInterface;
 
@@ -114,9 +115,9 @@ class SettingsForm extends ConfigFormBase {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    $scheme = file_default_scheme();
+    $scheme = \Drupal::config('system.file')->get('default_scheme');
     $directory = $scheme . '://' . $form_state->getValue('imagecache_directory');
-    if (!file_prepare_directory($directory, FILE_CREATE_DIRECTORY)) {
+    if (!\Drupal::service('file_system')->prepareDirectory($directory, FileSystemInterface::CREATE_DIRECTORY)) {
       $error = $this->t('The directory %directory does not exist or is not writable.', ['%directory' => $directory]);
       $form_state->setErrorByName('imagecache_directory', $error);
       $this->logger('imagecache_external')->error($error);