diff --git a/dhcp_tools/detail_wnd.c b/dhcp_tools/detail_wnd.c
index d054f1a..b90aa6b 100644
--- a/dhcp_tools/detail_wnd.c
+++ b/dhcp_tools/detail_wnd.c
@@ -170,7 +170,7 @@ static void create_dhcp_tree_mode(U8 *pkg, U32 nBytes, GtkWidget *treeView) {
     switch (get_package_vlan_type(pkg)) {
         default:
             pIp   = (struct iphdr *)(pkg + IP_HDR_OFFSET);
-            pUdp  = (struct udphdr *)(UDP_HDR_OFFSET);
+            pUdp  = (struct udphdr *)(pkg + UDP_HDR_OFFSET);
             pDhcp = (PDHCP_PROTO)((U8 *)pkg + DHCP_OFFSET);
             break;
         case VLAN_LEVEL1: