diff --git a/includes/file.inc b/includes/file.inc
index c0ce7c5942cedc68f2e68c4a5150014996e6b709..c0e68f52ebeb7f36106aa0b7ee01cf1d94ddb834 100644
--- a/includes/file.inc
+++ b/includes/file.inc
@@ -1067,7 +1067,7 @@ function file_space_used($uid = NULL, $status = FILE_STATUS_PERMANENT) {
  * the status and use file_save() to save the changes.
  *
  * @param $source
- *   A string specifying the filepath or URI of the upload field to save.
+ *   A string specifying the filepath or URI of the uploaded file to save.
  * @param $validators
  *   An optional, associative array of callback functions used to validate the
  *   file. See file_validate() for a full discussion of the array format.
@@ -1163,6 +1163,10 @@ function file_save_upload($source, $validators = array(), $destination = FALSE,
   }
 
   $file->source = $source;
+  // A URI may already have a trailing slash or look like "public://".
+  if (substr($destination, -1) != '/') {
+    $destination .= '/';
+  }
   $file->destination = file_destination($destination . $file->filename, $replace);
   // If file_destination() returns FALSE then $replace == FILE_EXISTS_ERROR and
   // there's an existing file so we need to bail.
diff --git a/modules/simpletest/tests/file.test b/modules/simpletest/tests/file.test
index 26bb051547f297e9e8fa9f35c109542555038672..2830e7b7ba07df1c9afab9cffe5b734573a35164 100644
--- a/modules/simpletest/tests/file.test
+++ b/modules/simpletest/tests/file.test
@@ -603,11 +603,23 @@ class FileSaveUploadTest extends FileHookTestCase {
     $this->assertTrue(isset($files[$file1->fid]), t('File was loaded successfully'));
     $this->assertTrue(isset($files[$file2->fid]), t('File was loaded successfully'));
 
+    // Upload a third file to a subdirectory.
+    $image3 = current($this->drupalGetTestFiles('image'));
+    $image3_realpath = drupal_realpath($image3->uri);
+    $dir = $this->randomName();
+    $edit = array(
+      'files[file_test_upload]' => $image3_realpath,
+      'file_subdir' => $dir,
+    );
+    $this->drupalPost('file-test/upload', $edit, t('Submit'));
+    $this->assertResponse(200, t('Received a 200 response for posted test file.'));
+    $this->assertRaw(t('You WIN!'));
+    $this->assertTrue(is_file('temporary://' . $dir . '/' . trim(basename($image3_realpath))));
+
     // Check that file_load_multiple() with no arguments returns FALSE.
     $this->assertFalse(file_load_multiple(), t('No files were loaded.'));
   }
 
-
   /**
    * Test renaming when uploading over a file that already exists.
    */
diff --git a/modules/simpletest/tests/file_test.module b/modules/simpletest/tests/file_test.module
index 9670d1ab323ec597217c4d9c28462f704d6449cb..635576506c9eece6b56982b6344f8830b5420c71 100644
--- a/modules/simpletest/tests/file_test.module
+++ b/modules/simpletest/tests/file_test.module
@@ -54,6 +54,11 @@ function _file_test_form(&$form_state) {
     ),
     '#default_value' => FILE_EXISTS_RENAME,
   );
+  $form['file_subdir'] = array(
+    '#type' => 'textfield',
+    '#title' => 'Subdirectory for test image',
+    '#default_value' => '',
+  );
   $form['submit'] = array(
     '#type' => 'submit',
     '#value' => t('Submit'),
@@ -67,7 +72,14 @@ function _file_test_form(&$form_state) {
 function _file_test_form_submit(&$form, &$form_state) {
   // Process the upload and validate that it is an image. Note: we're using the
   // form value for the $replace parameter.
-  $file = file_save_upload('file_test_upload', array('file_validate_is_image' => array()), FALSE, $form_state['values']['file_test_replace']);
+  if (!empty($form_state['values']['file_subdir'])) {
+    $destination = 'temporary://' . $form_state['values']['file_subdir'];
+    file_prepare_directory($destination, FILE_CREATE_DIRECTORY);
+  }
+  else {
+    $destination = FALSE;
+  }
+  $file = file_save_upload('file_test_upload', array('file_validate_is_image' => array()), $destination, $form_state['values']['file_test_replace']);
   if ($file) {
     $form_state['values']['file_test_upload'] = $file;
     drupal_set_message(t('File @filepath was uploaded.', array('@filepath' => $file->uri)));