diff --git a/modules/user/user.module b/modules/user/user.module
index 6cb7e7a..8f802c4 100644
--- a/modules/user/user.module
+++ b/modules/user/user.module
@@ -914,16 +914,16 @@ function user_permission() {
  */
 function user_impersonate_user($new_user = NULL) {
   global $user;
-  $user_original = &drupal_static(__FUNCTION__);
+  $user_original = &drupal_static(__FUNCTION__, array());
 
   if (!isset($new_user)) {
-    if (isset($user_original) && !empty($user_original)) {
+    if (!empty($user_original)) {
       // Restore the previous user from the stack.
       $user = array_pop($user_original);
 
       // Re-enable session saving if we are no longer impersonating a user.
       if (empty($user_original)) {
-        drupal_save_session(TRUE);
+        drupal_save_session();
       }
     }
   }
diff --git a/modules/user/user.test b/modules/user/user.test
index f7c893c..ddaad96 100644
--- a/modules/user/user.test
+++ b/modules/user/user.test
@@ -2329,6 +2329,7 @@ class UserImpersonatingUserTestCase extends DrupalWebTestCase {
   function testUserImpersonateUser() {
     global $user;
     $original_user = $user;
+    $original_session_saving = drupal_save_session();
 
     // If not currently logged in, use user_user_impersonate_user() to switch to
     // user 1. If logged in, switch to the anonymous user instead.
@@ -2369,7 +2370,9 @@ class UserImpersonatingUserTestCase extends DrupalWebTestCase {
     // Simpletest to enable session saving again. This is safe because calling
     // user_revert_user() too often simply results in returning the active user.
     user_revert_user();
-    $this->assertTrue(drupal_save_session(), t('Session saving is enabled.'));
+    $this->assertEqual(drupal_save_session(), $original_session_saving, t('Session saving is @status.', array(
+      '@status' => $original_session_saving ? t('enabled') : t('disabled'),
+    )));
   }
 }