diff --git a/bbs/visit_insert.inc.php b/bbs/visit_insert.inc.php
index 4aa235bd3..28232b330 100644
--- a/bbs/visit_insert.inc.php
+++ b/bbs/visit_insert.inc.php
@@ -14,7 +14,9 @@ if (get_cookie('ck_visit_ip') != $_SERVER['REMOTE_ADDR'])
     $referer = "";
     if (isset($_SERVER['HTTP_REFERER']))
         $referer = escape_trim(clean_xss_tags(strip_tags($_SERVER['HTTP_REFERER'])));
-    $user_agent  = escape_trim(clean_xss_tags(strip_tags($_SERVER['HTTP_USER_AGENT'])));
+    $user_agent = '';
+    if (isset($_SERVER['HTTP_USER_AGENT']))
+        $user_agent  = escape_trim(clean_xss_tags(strip_tags($_SERVER['HTTP_USER_AGENT'])));
     $vi_browser = '';
     $vi_os = '';
     $vi_device = '';