diff --git a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
index 7be618c13c8..35211cbf84b 100644
--- a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
+++ b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
@@ -330,6 +330,12 @@ class FileUploadResource extends ResourceBase {
     }
 
     $file->setFileUri($file_uri);
+    // Update the filename with any changes as a result of security or renaming
+    // due to an existing file.
+    // @todo Remove this duplication by replacing with FileUploadHandler. See
+    // https://www.drupal.org/project/drupal/issues/3401734
+    $file->setFilename($this->fileSystem->basename($file->getFileUri()));
+
     // Move the file to the correct location after validation. Use
     // FileSystemInterface::EXISTS_ERROR as the file location has already been
     // determined above in FileSystem::getDestinationFilename().
diff --git a/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php b/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
index 864f5e36810..7e348af06d8 100644
--- a/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
+++ b/core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
@@ -245,6 +245,13 @@ class TemporaryJsonapiFileFieldUploader {
     }
 
     $file->setFileUri($file_uri);
+
+    // Update the filename with any changes as a result of security or renaming
+    // due to an existing file.
+    // @todo Remove this duplication by replacing with FileUploadHandler. See
+    // https://www.drupal.org/project/drupal/issues/3401734
+    $file->setFilename($this->fileSystem->basename($file->getFileUri()));
+
     // Move the file to the correct location after validation. Use
     // FileSystemInterface::EXISTS_ERROR as the file location has already been
     // determined above in FileSystem::getDestinationFilename().
diff --git a/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php b/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php
index d028d094992..07f9dedd807 100644
--- a/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php
@@ -249,7 +249,7 @@ class FileUploadTest extends ResourceTestBase {
     // header with no 'file' prefix.
     $response = $this->fileRequest($uri, $this->testFileData, ['Content-Disposition' => 'filename="example.txt"']);
     $this->assertSame(201, $response->getStatusCode());
-    $expected = $this->getExpectedDocument(2, 'example_0.txt');
+    $expected = $this->getExpectedDocument(2, 'example_0.txt', TRUE);
     $this->assertResponseData($expected, $response);
 
     // Check the actual file data.
@@ -340,7 +340,7 @@ class FileUploadTest extends ResourceTestBase {
       'data' => [
         0 => $this->getExpectedDocument(1, 'existing.txt', TRUE, TRUE)['data'],
         1 => $this->getExpectedDocument(2, 'example.txt', TRUE, TRUE)['data'],
-        2 => $this->getExpectedDocument(3, 'example_0.txt', FALSE, TRUE)['data'],
+        2 => $this->getExpectedDocument(3, 'example_0.txt', TRUE, TRUE)['data'],
       ],
     ];
     $this->assertResponseData($expected, $response);
@@ -448,7 +448,7 @@ class FileUploadTest extends ResourceTestBase {
     $this->assertSame(201, $response->getStatusCode());
 
     // Loading expected normalized data for file 2, the duplicate file.
-    $expected = $this->getExpectedDocument(2, 'example_0.txt');
+    $expected = $this->getExpectedDocument(2, 'example_0.txt', TRUE);
     $this->assertResponseData($expected, $response);
 
     // Check the actual file data.
diff --git a/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
index 7ca019aeda1..712250ed82d 100644
--- a/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
@@ -195,7 +195,7 @@ abstract class FileUploadResourceTestBase extends ResourceTestBase {
     // header with no 'file' prefix.
     $response = $this->fileRequest($uri, $this->testFileData, ['Content-Disposition' => 'filename="example.txt"']);
     $this->assertSame(201, $response->getStatusCode());
-    $expected = $this->getExpectedNormalizedEntity(2, 'example_0.txt');
+    $expected = $this->getExpectedNormalizedEntity(2, 'example_0.txt', TRUE);
     $this->assertResponseData($expected, $response);
 
     // Check the actual file data.
@@ -317,7 +317,7 @@ abstract class FileUploadResourceTestBase extends ResourceTestBase {
     $this->assertSame(201, $response->getStatusCode());
 
     // Loading expected normalized data for file 2, the duplicate file.
-    $expected = $this->getExpectedNormalizedEntity(2, 'example_0.txt');
+    $expected = $this->getExpectedNormalizedEntity(2, 'example_0.txt', TRUE);
     $this->assertResponseData($expected, $response);
 
     // Check the actual file data.