diff --git a/core/includes/file.inc b/core/includes/file.inc
index 7d907cf..0c320fb 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -1067,12 +1067,9 @@ function file_save_upload($source, $validators = array(), $destination = FALSE,
   global $user;
   static $upload_cache;
 
-  // Prepare uploaded files info. Representation is slightly different
-  // for multiple uploads and we fix that here.
-  $uploaded_files = $_FILES;
-  if (!is_array($uploaded_files['files']['name'][$source])) {
-    foreach (array('name', 'type', 'tmp_name', 'error', 'size') as $value)
-    $uploaded_files['files'][$value][$source] = array($uploaded_files['files'][$value][$source]);
+  // Make sure there's an upload to process.
+  if (empty($_FILES['files']['name'][$source])) {
+    return NULL;
   }
 
   // Return cached objects without processing since the file will have
@@ -1084,9 +1081,12 @@ function file_save_upload($source, $validators = array(), $destination = FALSE,
     return $upload_cache[$source];
   }
 
-  // Make sure there's an upload to process.
-  if (empty($uploaded_files['files']['name'][$source][0])) {
-    return NULL;
+  // Prepare uploaded files info. Representation is slightly different
+  // for multiple uploads and we fix that here.
+  $uploaded_files = $_FILES;
+  if (!is_array($uploaded_files['files']['name'][$source])) {
+    foreach (array('name', 'type', 'tmp_name', 'error', 'size') as $value)
+    $uploaded_files['files'][$value][$source] = array($uploaded_files['files'][$value][$source]);
   }
 
   $files = array();
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileFieldTestBase.php b/core/modules/file/lib/Drupal/file/Tests/FileFieldTestBase.php
index c2d922d..855cec3 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileFieldTestBase.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileFieldTestBase.php
@@ -148,7 +148,12 @@ function uploadNodeFile($file, $field_name, $nid_or_type, $new_revision = TRUE,
     }
 
     // Attach a file to the node.
-    $edit['files[' . $field_name . '_' . $langcode . '_0]'] = drupal_realpath($file->uri);
+    $field = field_info_field($field_name);
+    $name = 'files[' . $field_name . '_' . $langcode . '_0]';
+    if ($field['cardinality'] != 1) {
+      $name .= '[]';
+    }
+    $edit[$name] = drupal_realpath($file->uri);
     $this->drupalPost("node/$nid/edit", $edit, t('Save and keep published'));
 
     return $nid;
diff --git a/core/modules/file/lib/Drupal/file/Tests/FileFieldWidgetTest.php b/core/modules/file/lib/Drupal/file/Tests/FileFieldWidgetTest.php
index b29144e..440840f 100644
--- a/core/modules/file/lib/Drupal/file/Tests/FileFieldWidgetTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/FileFieldWidgetTest.php
@@ -113,7 +113,7 @@ function testMultiValuedWidget() {
       $this->drupalGet("node/add/$type_name");
       foreach (array($field_name2, $field_name) as $each_field_name) {
         for ($delta = 0; $delta < 3; $delta++) {
-          $edit = array('files[' . $each_field_name . '_' . LANGUAGE_NOT_SPECIFIED . '_' . $delta . ']' => drupal_realpath($test_file->uri));
+          $edit = array('files[' . $each_field_name . '_' . LANGUAGE_NOT_SPECIFIED . '_' . $delta . '][]' => drupal_realpath($test_file->uri));
           // If the Upload button doesn't exist, drupalPost() will automatically
           // fail with an assertion message.
           $this->drupalPost(NULL, $edit, t('Upload'));
@@ -272,7 +272,7 @@ function testPrivateFileComment() {
     // Add a comment with a file.
     $text_file = $this->getTestFile('text');
     $edit = array(
-      'files[field_' . $name . '_' . LANGUAGE_NOT_SPECIFIED . '_' . 0 . '][]' => drupal_realpath($text_file->uri),
+      'files[field_' . $name . '_' . LANGUAGE_NOT_SPECIFIED . '_' . 0 . ']' => drupal_realpath($text_file->uri),
       'comment_body[' . LANGUAGE_NOT_SPECIFIED . '][0][value]' => $comment_body = $this->randomName(),
     );
     $this->drupalPost(NULL, $edit, t('Save'));