core/modules/file/src/Plugin/rest/resource/FileUploadResource.php     | 2 +-
 core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
index 2d73a79..51f536f 100644
--- a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
+++ b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
@@ -162,7 +162,7 @@ public function post(Request $request, $entity_type_id, $bundle, $field_name) {
     }
 
     // Create the file.
-    $file_uri = "{$destination}{$filename}";
+    $file_uri = "{$destination}/{$filename}";
 
     $this->streamUploadData($file_uri);
 
diff --git a/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php b/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php
index 05d467e..15cfa09 100644
--- a/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php
+++ b/core/modules/file/tests/src/Functional/FileUploadResourceTestBase.php
@@ -214,7 +214,7 @@ public function testPostFileUpload() {
       ],
       'uri' => [
         [
-          'value' => 'public://foobarexample.txt',
+          'value' => 'public://foobar/example.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://foobarexample.txt'));
+    $this->assertSame($file_data, file_get_contents('public://foobar/example.txt'));
   }
 
   /**