| diff --git a/scapy/contrib/cdp.py b/scapy/contrib/cdp.py | |
| index a1532b78..83963ff4 100644 | |
| --- a/scapy/contrib/cdp.py | |
| +++ b/scapy/contrib/cdp.py | |
| @@ -392,7 +392,7 @@ class _CDPChecksum: | |
| This padding is only used for checksum computation. The original | |
| packet should not be altered.""" | |
| if len(pkt) % 2: | |
| - last_chr = orb(pkt[-1]) | |
| + last_chr = orb(pkt[len(pkt)-1:]) | |
| if last_chr <= 0x80: | |
| return pkt[:-1] + b'\x00' + chb(last_chr) | |
| else: | |