diff --git a/mongodb_session/mongodb_session.module b/mongodb_session/mongodb_session.module
index 09342f3..f930df3 100644
--- a/mongodb_session/mongodb_session.module
+++ b/mongodb_session/mongodb_session.module
@@ -19,7 +19,8 @@ function mongodb_session_simpletest_alter(&$groups) {
  */
 function mongodb_session_user_update($edit, $account) {
   // Update field values for changed values of the user.
-  if (module_exists('mongodb_field_storage')) {
+  $field_storage = variable_get('field_storage_default', 'field_sql_storage');
+  if ($field_storage == 'mongodb_field_storage') {
     $roles = _mongodb_session_get_roles($account);
     $save = (array) $account + array(
       '_id' => (int) $account->uid,