core/modules/file/src/Plugin/rest/resource/FileUploadResource.php   | 2 +-
 .../file/tests/src/Functional/FileUploadResourceTestBase.php        | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
index adae53f..2d73a79 100644
--- a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
+++ b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
@@ -157,7 +157,7 @@ public function post(Request $request, $entity_type_id, $bundle, $field_name) {
     }
 
     // Check the destination file path is writable.
-    if (!is_writable($this->fileSystem->realpath($destination))) {
+    if (!file_prepare_directory($destination, FILE_CREATE_DIRECTORY)) {
       throw new HttpException(500, 'Destination file path is not writable');
     }
 
diff --git a/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php b/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php
index a446349..05d467e 100644
--- a/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php
+++ b/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php
@@ -87,7 +87,7 @@ public function setUp() {
       'field_name' => 'field_rest_file_test',
       'bundle' => 'entity_test',
       'settings' => [
-        'file_directory' => '',
+        'file_directory' => 'foobar',
         'file_extensions' => 'txt',
         'max_filesize' => '',
       ],
@@ -214,7 +214,7 @@ public function testPostFileUpload() {
       ],
       'uri' => [
         [
-          'value' => 'public://example.txt',
+          'value' => 'public://foobarexample.txt',
         ],
       ],
       'filemime' => [
@@ -242,7 +242,7 @@ public function testPostFileUpload() {
     $this->assertSame($expected_normalization, $this->serializer->decode((string) $response->getBody(), static::$format));
 
     // Check the actual file data.
-    $this->assertSame($file_data, file_get_contents('public://example.txt'));
+    $this->assertSame($file_data, file_get_contents('public://foobarexample.txt'));
   }
 
   /**