diff --git a/web/template/syzoj/problemset.php b/web/template/syzoj/problemset.php
index 7bb3d50..0645479 100644
--- a/web/template/syzoj/problemset.php
+++ b/web/template/syzoj/problemset.php
@@ -96,11 +96,17 @@
       $section = 8;
       $start = $page > $section ? $page - $section : 1;
       $end = $page + $section > $view_total_page ? $view_total_page : $page + $section;
+      function get_query_user_id($query_user_id)
+      {
+        if (!isset($query_user_id))
+          return "";
+        return "&query_user_id=" . $query_user_id;
+      }
       function get_href($page, $postfix, $query_user_id)
       {
         return "problemset.php?page=" . $page .
           htmlentities($postfix, ENT_QUOTES, 'UTF-8') .
-          "&query_user_id=" . $query_user_id;
+          get_query_user_id($query_user_id);
       }
       ?>
       <div style="text-align: center; ">