diff --git a/scapy/layers/inet6.py b/scapy/layers/inet6.py
index 58720b79ea3..4e91071bfce 100644
--- a/scapy/layers/inet6.py
+++ b/scapy/layers/inet6.py
@@ -996,16 +996,21 @@ class IPv6ExtHdrDestOpt(_IPv6ExtHdr):
 class IPv6ExtHdrRouting(_IPv6ExtHdr):
     name = "IPv6 Option Header Routing"
     fields_desc = [ByteEnumField("nh", 59, ipv6nh),
-                   FieldLenField("len", None, count_of="addresses", fmt="B",
-                                 adjust=lambda pkt, x:2 * x),  # in 8 bytes blocks  # noqa: E501
+                   ByteField("len", None),  # in 8 bytes blocks
                    ByteField("type", 0),
                    ByteField("segleft", None),
                    BitField("reserved", 0, 32),  # There is meaning in this field ...  # noqa: E501
                    IP6ListField("addresses", [],
-                                length_from=lambda pkt: 8 * pkt.len)]
+                                length_from=lambda pkt: 16 * (pkt.len // 2)),
+                   # An odd 'len' leaves 8 bytes over, which is half an address.
+                   StrLenField("pad", b"",
+                               length_from=lambda pkt: 8 * (pkt.len % 2))]
     overload_fields = {IPv6: {"nh": 43}}
 
     def post_build(self, pkt, pay):
+        if self.len is None:
+            tmp_len = (len(pkt) - 8) // 8
+            pkt = pkt[:1] + struct.pack("B", tmp_len) + pkt[2:]
         if self.segleft is None:
             pkt = pkt[:3] + struct.pack("B", len(self.addresses)) + pkt[4:]
         return _IPv6ExtHdr.post_build(self, pkt, pay)
diff --git a/test/scapy/layers/inet6.uts b/test/scapy/layers/inet6.uts
index 16d56d7ff88..2a3a5575808 100644
--- a/test/scapy/layers/inet6.uts
+++ b/test/scapy/layers/inet6.uts
@@ -81,6 +81,19 @@ raw(IPv6(src="2048::deca", dst="2047::cafe")/IPv6ExtHdrRouting(addresses=["2001:
 
 ########### IPv6ExtHdrSegmentRouting Class ###########################
 
+= IPv6ExtHdrRouting Class - Odd length - build and dissect
+routing = IPv6ExtHdrRouting(type=253, segleft=0, pad=b"12345678")
+# Port 5353 would make Scapy parse the payload as mDNS; the point here is the
+# routing header, so use a port with no higher-layer binding.
+s = raw(IPv6(src="2001:db8::1", dst="2001:db8::2") / routing /
+        UDP(sport=53000, dport=40000) / Raw(b"policy"))
+p = IPv6(s)
+assert p[IPv6ExtHdrRouting].len == 1
+assert p[IPv6ExtHdrRouting].addresses == []
+assert p[IPv6ExtHdrRouting].pad == b"12345678"
+assert UDP in p and p[UDP].dport == 40000
+assert raw(p) == s
+
 = IPv6ExtHdrSegmentRouting Class - default - build & dissect
 s = raw(IPv6()/IPv6ExtHdrSegmentRouting()/UDP())
 assert s == b'`\x00\x00\x00\x00 +@\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x11\x02\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x005\x005\x00\x08\xffr'