diff --git a/core/modules/simpletest/tests/module.test b/core/modules/simpletest/tests/module.test
index 19acf60..440bf2f 100644
--- a/core/modules/simpletest/tests/module.test
+++ b/core/modules/simpletest/tests/module.test
@@ -239,6 +239,34 @@ class ModuleUnitTest extends DrupalWebTestCase {
 }
 
 /**
+ * Tests whether the correct module metadata is returned.
+ */
+function testModuleMetaData() {
+  // Generate the list of available modules.
+  $modules = system_rebuild_module_data();
+  // Check that the mtime field exists for the system module.
+  $this->assertTrue(!empty($modules['system']->info['mtime']), 'The system.info file modification time field is present.');
+  // Use 0 if mtime isn't present, to avoid an array index notice.
+  $test_mtime = !empty($modules['system']->info['mtime']) ? $modules['system']->info['mtime'] : 0;
+  // Ensure the mtime field contains a number that is greater than zero.
+  $this->assertTrue(is_numeric($test_mtime) && ($test_mtime > 0), 'The system.info file modification time field contains a timestamp.');
+}
+
+/**
+ * Tests whether the correct theme metadata is returned.
+ */
+function testThemeMetaData() {
+  // Generate the list of available themes.
+  $themes = system_rebuild_theme_data();
+  // Check that the mtime field exists for the system module.
+  $this->assertTrue(!empty($themes['bartik']->info['mtime']), 'The bartik.info file modification time field is present.');
+  // Use 0 if mtime isn't present, to avoid an array index notice.
+  $test_mtime = !empty($themes['bartik']->info['mtime']) ? $themes['bartik']->info['mtime'] : 0;
+  // Ensure the mtime field contains a number that is greater than zero.
+  $this->assertTrue(is_numeric($test_mtime) && ($test_mtime > 0), 'The bartik.info file modification time field contains a timestamp.');
+}
+
+/**
  * Tests class loading.
  */
 class ModuleClassLoaderTestCase extends DrupalWebTestCase {
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 151d299..1a2d9b2 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2425,6 +2425,10 @@ function _system_rebuild_module_data() {
     // Look for the info file.
     $module->info = drupal_parse_info_file(dirname($module->uri) . '/' . $module->name . '.info');
 
+    // Add the info file modification time, so the modules page can be sorted
+    // by the date modules were added or updated.
+    $module->info['mtime'] = filemtime(dirname($module->uri) . '/' . $module->name . '.info');
+
     // Skip modules that don't provide info.
     if (empty($module->info)) {
       unset($modules[$key]);
@@ -2569,6 +2573,10 @@ function _system_rebuild_theme_data() {
     $themes[$key]->filename = $theme->uri;
     $themes[$key]->info = drupal_parse_info_file($theme->uri) + $defaults;
 
+    // Add the info file modification time, so the themes page can be sorted
+    // by the date themes were added or updated.
+    $themes[$key]->info['mtime'] = filemtime($theme->uri);
+
     // Invoke hook_system_info_alter() to give installed modules a chance to
     // modify the data in the .info files if necessary.
     $type = 'theme';