diff -u b/core/includes/file.inc b/core/includes/file.inc
--- b/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -2412,38 +2412,17 @@
 }
 
 /**
- * Gets the path of system-appropriate temporary directory.
+ * Gets and sets the path of the configured temporary directory.
+ *
+ * @return
+ *   A sting containing path to temporary directory.
  */
 function file_directory_temp() {
   $config = config('system.file');
   $temporary_directory = $config->get('path.temporary');
 
   if (empty($temporary_directory)) {
-    $directories = array();
-
-    // Has PHP been set with an upload_tmp_dir?
-    if (ini_get('upload_tmp_dir')) {
-      $directories[] = ini_get('upload_tmp_dir');
-    }
-
-    // Operating system specific dirs.
-    if (substr(PHP_OS, 0, 3) == 'WIN') {
-      $directories[] = 'c:\\windows\\temp';
-      $directories[] = 'c:\\winnt\\temp';
-    }
-    else {
-      $directories[] = '/tmp';
-    }
-    // PHP may be able to find an alternative tmp directory.
-    $directories[] = sys_get_temp_dir();
-
-    foreach ($directories as $directory) {
-      if (is_dir($directory) && is_writable($directory)) {
-        $temporary_directory = $directory;
-        break;
-      }
-    }
-
+    $temporary_directory = file_directory_system_temp();
     if (empty($temporary_directory)) {
       // If no directory has been found default to 'files/tmp'.
       $temporary_directory = $config->get('path.public') . '/tmp';
@@ -2462,6 +2441,39 @@
 }
 
 /**
+ * Discovers a writable system-appropriate temporary directory.
+ *
+ * @return
+ *   A sting containing path to temporary directory.
+ */
+function file_directory_system_temp() {
+  $directories = array();
+
+  // Has PHP been set with an upload_tmp_dir?
+  if (ini_get('upload_tmp_dir')) {
+    $directories[] = ini_get('upload_tmp_dir');
+  }
+
+  // Operating system specific dirs.
+  if (substr(PHP_OS, 0, 3) == 'WIN') {
+    $directories[] = 'c:\\windows\\temp';
+    $directories[] = 'c:\\winnt\\temp';
+  }
+  else {
+    $directories[] = '/tmp';
+  }
+  // PHP may be able to find an alternative tmp directory.
+  $directories[] = sys_get_temp_dir();
+
+  foreach ($directories as $directory) {
+    if (is_dir($directory) && is_writable($directory)) {
+      return $directory;
+    }
+  }
+  return FALSE;
+}
+
+/**
  * Examines a file entity and returns appropriate content headers for download.
  *
  * @param Drupal\Core\File\File $file
diff -u b/core/lib/Drupal/Core/StreamWrapper/TemporaryStream.php b/core/lib/Drupal/Core/StreamWrapper/TemporaryStream.php
--- b/core/lib/Drupal/Core/StreamWrapper/TemporaryStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/TemporaryStream.php
@@ -21,7 +21,7 @@
   public function getDirectoryPath() {
     $temporary_path = config('system.file')->get('path.temporary');
     if (empty($temporary_path)) {
-      $temporary_path = sys_get_temp_dir();
+      $temporary_path = file_directory_system_temp();
     }
     return $temporary_path;
   }
reverted:
--- b/core/modules/aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php
+++ a/core/modules/aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php
@@ -53,7 +53,6 @@
       'files[upload]' => $path,
       'remote' => file_create_url($path),
     );
-    $this->verbose("alex: " . config('system.file')->get('path.temporary'));
     $this->drupalPost('admin/config/services/aggregator/add/opml', $edit, t('Import'));
     $this->assertRaw(t('You must <em>either</em> upload a file or enter a URL.'), t('Error if both fields are filled.'));
 
diff -u b/core/modules/system/system.install b/core/modules/system/system.install
--- b/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -306,18 +306,28 @@
 
   // Test files directories.
   if ($phase != 'install') {
-    $filesystem_config = config('system.file');
-    $directories = array(
-      $filesystem_config->get('path.public'),
-      // By default no private files directory is configured. For private files
-      // to be secure the admin needs to provide a path outside the webroot.
-      $filesystem_config->get('path.private'),
-      file_directory_temp(),
-    );
+    $config_installed = db_table_exists('config');
+    if ($phase == 'update' && !$config_installed) {
+      // Updating from 7 to 8.
+      // @TODO
+      // Use new functions from http://drupal.org/node/1348162 to load Drupal 7
+      // variables or use Drupal 7 defaults to create $directories array.
+    }
+    else {
+      $filesystem_config = config('system.file');
+      $directories = array(
+        $filesystem_config->get('path.public'),
+        // By default no private files directory is configured. For private files
+        // to be secure the admin needs to provide a path outside the webroot.
+        $filesystem_config->get('path.private'),
+        file_directory_temp(),
+      );
+    }
   }
-  else {
-    // During an install we need to make assumptions about the file system
-    // unless overrides are provided in settings.php.
+
+  // During an install we need to make assumptions about the file system
+  // unless overrides are provided in settings.php.
+  if ($phase == 'install') {
     $directories = array();
     if (!empty($GLOBALS['system.file.path.public'])) {
       $directories[] = $GLOBALS['system.file.path.public'];
@@ -335,7 +345,9 @@
       $directories[] = $GLOBALS['system.file.path.temporary'];
     }
     else {
-      $directories[] = sys_get_temp_dir();
+      // If temporary directory not overriden use an appropriate temporary for
+      // the system.
+      $directories[] = file_directory_system_temp();
     }
   }