reverted:
--- b/core/includes/file.inc
+++ a/core/includes/file.inc
@@ -524,7 +524,7 @@
   else {
     // Perhaps $destination is a dir/file?
     $dirname = drupal_dirname($destination);
+    if (!file_prepare_directory($dirname)) {
-    if (!file_prepare_directory($dirname, FILE_CREATE_DIRECTORY)) {
       // The destination is not valid.
       $logger->notice('File %file could not be moved/copied because the destination directory %destination is not configured correctly.', array('%file' => $original_source, '%destination' => $dirname));
       drupal_set_message(t('The specified file %file could not be moved/copied because the destination directory is not properly configured. This may be caused by a problem with file or directory permissions. More information is available in the system log.', array('%file' => $original_source)), 'error');
diff -u b/core/tests/Drupal/KernelTests/Core/File/UnmanagedCopyTest.php b/core/tests/Drupal/KernelTests/Core/File/UnmanagedCopyTest.php
--- b/core/tests/Drupal/KernelTests/Core/File/UnmanagedCopyTest.php
+++ b/core/tests/Drupal/KernelTests/Core/File/UnmanagedCopyTest.php
@@ -37,7 +37,23 @@
     $this->assertTrue(file_exists($newer_filepath), 'New file exists.');
     $this->assertFilePermissions($newer_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
 
-    // TODO: test copying to a directory (rather than full directory/file path)
+    // Copying to an existing directory.
+    $desired_directory = 'public://' . $this->randomMachineName();
+    $this->assertFalse(file_exists($desired_directory), 'Directory does not exist.');
+    $this->assertTrue(file_prepare_directory($desired_directory, FILE_CREATE_DIRECTORY), 'Directory was created.');
+    $desired_filepath = $desired_directory . DIRECTORY_SEPARATOR . $this->randomMachineName();
+    $newer_filepath = file_unmanaged_copy($uri, $desired_filepath, FILE_EXISTS_ERROR);
+    $this->assertTrue($newer_filepath, 'Copy was successful.');
+    $this->assertTrue(file_exists($newer_filepath), 'New file exists.');
+
+    // Copying to a missing directory.
+    $desired_directory = 'public://' . $this->randomMachineName();
+    $this->assertFalse(file_exists($desired_directory), 'Directory does not exist.');
+    $desired_filepath = $desired_directory . DIRECTORY_SEPARATOR . $this->randomMachineName();
+    $newer_filepath = file_unmanaged_copy($uri, $desired_filepath, FILE_EXISTS_ERROR);
+    $this->assertFalse($newer_filepath, 'Copy was not successful.');
+    $this->assertFalse(file_exists($newer_filepath), 'New file does not exist.');
+
     // TODO: test copying normal files using normal paths (rather than only streams)
   }
 
@@ -84,14 +100,6 @@
     $this->assertTrue(file_exists($uri), 'Original file exists after copying onto itself.');
     $this->assertTrue(file_exists($new_filepath), 'Copied file exists after copying onto itself.');
     $this->assertFilePermissions($new_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
-
-    // Copy the file into a subdirectory that does not exist.
-    $new_filepath = file_unmanaged_copy($uri, \Drupal::service('file_system')->dirname($uri) . '/sub/' . \Drupal::service('file_system')->basename($uri), FILE_EXISTS_ERROR);
-    $this->assertTrue($new_filepath, 'Copying into same directory works.');
-    self::assertNotEquals($new_filepath, $uri, 'Copied file has a new name.');
-    $this->assertTrue(file_exists($uri), 'Original file exists after copying onto itself.');
-    $this->assertTrue(file_exists($new_filepath), 'Copied file exists after copying onto itself.');
-    $this->assertFilePermissions($new_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
   }
 
 }
diff -u b/core/tests/Drupal/KernelTests/Core/File/UnmanagedMoveTest.php b/core/tests/Drupal/KernelTests/Core/File/UnmanagedMoveTest.php
--- b/core/tests/Drupal/KernelTests/Core/File/UnmanagedMoveTest.php
+++ b/core/tests/Drupal/KernelTests/Core/File/UnmanagedMoveTest.php
@@ -21,30 +21,46 @@
     // Moving to a new name.
     $desired_filepath = 'public://' . $this->randomMachineName();
     $new_filepath = file_unmanaged_move($uri, $desired_filepath, FILE_EXISTS_ERROR);
+    $this->assertTrue($new_filepath, 'Move was successful.');
     $this->assertEqual($new_filepath, $desired_filepath, 'Returned expected filepath.');
-    $this->assertFileExists($new_filepath, 'File exists at the new location.');
-    $this->assertFileNotExists($uri, 'No file remains at the old location.');
+    $this->assertTrue(file_exists($new_filepath), 'File exists at the new location.');
+    $this->assertFalse(file_exists($uri), 'No file remains at the old location.');
     $this->assertFilePermissions($new_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
 
     // Moving with rename.
+    $uri = $new_filepath;
     $desired_filepath = 'public://' . $this->randomMachineName();
-    $this->assertTrue(file_exists($new_filepath), 'File exists before moving.');
+    $this->assertTrue(file_exists($uri), 'File exists before moving.');
     $this->assertTrue(file_put_contents($desired_filepath, ' '), 'Created a file so a rename will have to happen.');
-    $newer_filepath = file_unmanaged_move($new_filepath, $desired_filepath, FILE_EXISTS_RENAME);
-    $this->assertNotEqual($newer_filepath, $desired_filepath, 'Returned expected filepath.');
-    $this->assertFileExists($newer_filepath, 'File exists at the new location.');
-    $this->assertFileNotExists($new_filepath, 'No file remains at the old location.');
-    $this->assertFilePermissions($newer_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
+    $new_filepath = file_unmanaged_move($uri, $desired_filepath, FILE_EXISTS_RENAME);
+    $this->assertTrue($new_filepath, 'Move was successful.');
+    $this->assertNotEqual($new_filepath, $desired_filepath, 'Returned expected filepath.');
+    $this->assertTrue(file_exists($new_filepath), 'File exists at the new location.');
+    $this->assertFalse(file_exists($uri), 'No file remains at the old location.');
+    $this->assertFilePermissions($new_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
+
+    // Moving to an existing directory.
+    $uri = $new_filepath;
+    $desired_directory = 'public://' . $this->randomMachineName();
+    $this->assertFalse(file_exists($desired_directory), 'Directory does not exist.');
+    $this->assertTrue(file_prepare_directory($desired_directory, FILE_CREATE_DIRECTORY), 'Directory was created.');
+    $desired_filepath = $desired_directory . DIRECTORY_SEPARATOR . $this->randomMachineName();
+    $new_filepath = file_unmanaged_move($uri, $desired_filepath, FILE_EXISTS_ERROR);
+    $this->assertTrue($new_filepath, 'Move was successful.');
+    $this->assertEqual($new_filepath, $desired_filepath, 'Returned expected filepath.');
+    $this->assertTrue(file_exists($new_filepath), 'File exists at the new location.');
+    $this->assertFalse(file_exists($uri), 'No file remains at the old location.');
 
-    // Moving the file into a subdirectory that does not exist.
-    $desired_filepath = 'public://sub/' . $this->randomMachineName();
-    $newest_filepath = file_unmanaged_move($newer_filepath, $desired_filepath, FILE_EXISTS_ERROR);
-    self::assertEquals($newest_filepath, $desired_filepath, 'Returned expected filepath.');
-    $this->assertFileExists($newest_filepath, 'File exists at the new location.');
-    $this->assertFileNotExists($newer_filepath, 'No file remains at the old location.');
-    $this->assertFilePermissions($newest_filepath, Settings::get('file_chmod_file', FileSystem::CHMOD_FILE));
+    // Moving to a missing directory.
+    $uri = $new_filepath;
+    $desired_directory = 'public://' . $this->randomMachineName();
+    $this->assertFalse(file_exists($desired_directory), 'Directory does not exist.');
+    $desired_filepath = $desired_directory . DIRECTORY_SEPARATOR . $this->randomMachineName();
+    $new_filepath = file_unmanaged_copy($uri, $desired_filepath, FILE_EXISTS_ERROR);
+    $this->assertFalse($new_filepath, 'Move was not successful.');
+    $this->assertFalse(file_exists($new_filepath), 'New file does not exist.');
+    $this->assertTrue(file_exists($uri), 'Original file remains.');
 
-    // TODO: test moving to a directory (rather than full directory/file path)
     // TODO: test creating and moving normal files (rather than streams)
   }