diff --git a/core/lib/Drupal/Core/File/UnmanagedFileHandler.php b/core/lib/Drupal/Core/File/UnmanagedFileHandler.php
index c06c6e6..843f635 100644
--- a/core/lib/Drupal/Core/File/UnmanagedFileHandler.php
+++ b/core/lib/Drupal/Core/File/UnmanagedFileHandler.php
@@ -6,7 +6,6 @@
 use Drupal\Core\File\Exception\FileException;
 use Drupal\Core\File\Exception\FileExistsException;
 use Drupal\Core\File\Exception\FileNotExistsException;
-use Drupal\Core\File\FileHandlerInterface;
 
 /**
  * Implements service for low-level unhandled file operations.
@@ -33,7 +32,7 @@ public function __construct(FileSystemInterface $file_system) {
   /**
    * {@inheritdoc}
    */
-  public function copy($source, $destination, $replace = FileSystemInterface::FILE_EXISTS_RENAME) {
+  public function copy($source, $destination, $replace = self::FILE_EXISTS_RENAME) {
     $this->prepare($source, $destination, $replace);
 
     // Perform the copy operation.
@@ -52,8 +51,7 @@ public function copy($source, $destination, $replace = FileSystemInterface::FILE
   }
 
   /**
-   * Internal function that prepares the destination for a file_unmanaged_copy or
-   * file_unmanaged_move operation.
+   * Prepares the destination for a file copy or move operation.
    *
    * - Checks if $source and $destination are valid and readable/writable.
    * - Checks that $source is not equal to $destination; if they are an error
@@ -63,7 +61,7 @@ public function copy($source, $destination, $replace = FileSystemInterface::FILE
    *
    * @internal
    *   This public method is marked internal in 8.3.x and will be
-   *   converted into private method before 9.0.0.
+   *   converted into protected method before 9.0.0.
    *
    * @param $source
    *   A string specifying the filepath or URI of the source file.
@@ -82,14 +80,21 @@ public function copy($source, $destination, $replace = FileSystemInterface::FILE
    * @return void
    *
    * @throws \Drupal\Core\File\Exception\DirectoryNotReadyException
+   *   When the destination directory is not properly configured.
+   *
    * @throws \Drupal\Core\File\Exception\FileException
+   *   When the source and destination are the same file.
+   *
    * @throws \Drupal\Core\File\Exception\FileExistsException
+   *   When a file by that name already exists in the destination directory.
+   *
    * @throws \Drupal\Core\File\Exception\FileNotExistsException
+   *   When the source file does not exist.
    *
    * @see \Drupal\Core\File\UnmanagedFileHandler::copy()
    * @see \Drupal\Core\File\UnmanagedFileHandler::move()
    */
-  public function prepare($source, &$destination = NULL, $replace = FileSystemInterface::FILE_EXISTS_RENAME) {
+  public function prepare($source, &$destination = NULL, $replace = self::FILE_EXISTS_RENAME) {
     $original_source = $source;
 
     // Assert that the source file actually exists.
diff --git a/core/lib/Drupal/Core/File/UnmanagedFileHandlerInterface.php b/core/lib/Drupal/Core/File/UnmanagedFileHandlerInterface.php
index e418cbd..248d6ca 100644
--- a/core/lib/Drupal/Core/File/UnmanagedFileHandlerInterface.php
+++ b/core/lib/Drupal/Core/File/UnmanagedFileHandlerInterface.php
@@ -46,9 +46,7 @@
    * @throws \Drupal\Core\File\Exception\FileException
    * @throws \Drupal\Core\File\Exception\FileExistsException
    * @throws \Drupal\Core\File\Exception\FileNotExistsException
-   *
-   * @see file_copy()
    */
-  public function copy($source, $destination, $replace = FileHandlerInterface::FILE_EXISTS_RENAME);
+  public function copy($source, $destination, $replace = self::FILE_EXISTS_RENAME);
 
 }