diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index 7fa42d0..3e708c9 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -2223,13 +2223,18 @@ function drupal_bootstrap($phase = NULL, $new_phase = TRUE) {
 function drupal_get_user_timezone() {
   global $user;
   if (variable_get('configurable_timezones', 1) && $user->uid && $user->timezone) {
-    return $user->timezone;
+    $timezone = $user->timezone;
   }
   else {
     // Ignore PHP strict notice if time zone has not yet been set in the php.ini
     // configuration.
-    return variable_get('date_default_timezone', @date_default_timezone_get());
+    $timezone = variable_get('date_default_timezone', @date_default_timezone_get());
   }
+  // check timezone whether is exists
+  if(!array_search($timezone, DateTimeZone::listIdentifiers())) {
+    $timezone = @date_default_timezone_get();
+  }
+  return $timezone;
 }
 
 /**