diff --git a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
index 7f840fb988..e4e44b6152 100644
--- a/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
+++ b/core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
@@ -181,7 +181,7 @@ public function post(Request $request, $entity_type_id, $bundle, $field_name) {
       'uri' => $file_uri,
       // Set the size. This is done in File::preSave() but we validate the file
       // before it is saved.
-      'size' => @filesize($file_uri),
+      'filesize' => @filesize($file_uri),
     ];
     $values['filemime'] = $this->mimeTypeGuesser->guess($values['filename']);
     $file = File::create($values);
diff --git a/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
index b6cb7c04c7..42a956ffcd 100644
--- a/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/FileUploadResourceTestBase.php
@@ -152,16 +152,62 @@ public function testPostFileUpload() {
     $this->assertSame(201, $response->getStatusCode());
 
     $expected = $this->getExpectedNormalizedEntity();
-    static::recursiveKSort($expected);
-    $actual = $this->serializer->decode((string) $response->getBody(), static::$format);
-    static::recursiveKSort($actual);
 
-    $this->assertSame($expected, $actual);
+    $this->assertResponseData($expected, $response);
 
     // Check the actual file data.
     $this->assertSame($this->testFileData, file_get_contents('public://foobar/example.txt'));
   }
 
+  /**
+   * Tests using the file upload route with a zero byte file.
+   */
+  public function testFileUploadZeroByteFile() {
+    $this->initAuthentication();
+
+    $this->provisionResource([static::$format], static::$auth ? [static::$auth] : [], ['POST']);
+
+    $this->setUpAuthorization('POST');
+
+    $uri = Url::fromUri('base:' . static::$postUri);
+
+    // Test with a zero byte file.
+    $response = $this->fileRequest($uri, NULL);
+
+    $this->assertSame(201, $response->getStatusCode());
+
+    $expected = $this->getExpectedNormalizedEntity();
+    // Modify the default expected data to account for the 0 byte file.
+    $expected['filesize'][0]['value'] = 0;
+
+    $this->assertResponseData($expected, $response);
+
+    // Check the actual file data.
+    $this->assertSame('', file_get_contents('public://foobar/example.txt'));
+  }
+
+  /**
+   * Tests using the file upload route with an invalid file type.
+   */
+  public function testFileUploadInvalidFileType() {
+    $this->initAuthentication();
+
+    $this->provisionResource([static::$format], static::$auth ? [static::$auth] : [], ['POST']);
+
+    $this->setUpAuthorization('POST');
+
+    $uri = Url::fromUri('base:' . static::$postUri);
+
+    // Test with a JSON file.
+    $response = $this->fileRequest($uri, '{"test":123}', ['Content-Disposition' => 'filename="example.json"']);
+
+    $this->assertSame(422, $response->getStatusCode());
+
+    // Make sure that no file was saved.
+    $this->assertEmpty(File::load(1));
+    $this->assertFalse(file_exists('public://foobar/example.txt'));
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -297,4 +343,20 @@ protected function setUpAuthorization($method) {
     }
   }
 
+  /**
+   * Asserts expected normalized data matches response data.
+   *
+   * @param array $expected
+   *   The expected data.
+   * @param \Psr\Http\Message\ResponseInterface $response
+   *   The file upload response.
+   */
+  protected function assertResponseData(array $expected, ResponseInterface $response) {
+    static::recursiveKSort($expected);
+    $actual = $this->serializer->decode((string) $response->getBody(), static::$format);
+    static::recursiveKSort($actual);
+
+    $this->assertSame($expected, $actual);
+  }
+
 }