diff --git a/scapy/contrib/cdp.py b/scapy/contrib/cdp.py
index c8b7f106..7b1ff64d 100644
--- a/scapy/contrib/cdp.py
+++ b/scapy/contrib/cdp.py
@@ -102,7 +102,8 @@ def _CDPGuessPayloadClass(p, **kargs):
 class CDPMsgGeneric(Packet):
     name = "CDP Generic Message"
     fields_desc = [ XShortEnumField("type", None, _cdp_tlv_types),
-                    FieldLenField("len", None, "val", "!H"),
+                    FieldLenField("len", None, "val", "!H",
+                                  adjust=lambda pkt, x: x + 4),
                     StrLenField("val", "", length_from=lambda x:x.len - 4) ]
 
 
@@ -178,7 +179,8 @@ class CDPMsgAddr(CDPMsgGeneric):
 class CDPMsgPortID(CDPMsgGeneric):
     name = "Port ID"
     fields_desc = [ XShortEnumField("type", 0x0003, _cdp_tlv_types),
-                    FieldLenField("len", None, "iface", "!H"),
+                    FieldLenField("len", None, "iface", "!H",
+                                  adjust=lambda pkt, x: x + 4),
                     StrLenField("iface", "Port 1", length_from=lambda x:x.len - 4) ]