diff --git a/wire/message_test.go b/wire/message_test.go
index 06aa81505a..19db98edc8 100644
--- a/wire/message_test.go
+++ b/wire/message_test.go
@@ -83,7 +83,7 @@ func TestMessage(t *testing.T) {
 	if err != nil {
 		t.Errorf("NewMsgMixPairReq: %v", err)
 	}
-	msgMixKE := NewMsgMixKeyExchange([33]byte{}, [32]byte{}, 1, 1, [33]byte{}, [1218]byte{}, [32]byte{}, []chainhash.Hash{})
+	msgMixKE := NewMsgMixKeyExchange([33]byte{}, [32]byte{}, 1, 1, 1, [33]byte{}, [1218]byte{}, [32]byte{}, []chainhash.Hash{})
 	msgMixCT := NewMsgMixCiphertexts([33]byte{}, [32]byte{}, 1, [][1047]byte{}, []chainhash.Hash{})
 	msgMixSR := NewMsgMixSlotReserve([33]byte{}, [32]byte{}, 1, [][][]byte{{{}}}, []chainhash.Hash{})
 	msgMixFP := NewMsgMixFactoredPoly([33]byte{}, [32]byte{}, 1, [][]byte{}, []chainhash.Hash{})
@@ -122,7 +122,7 @@ func TestMessage(t *testing.T) {
 		{msgGetInitState, msgGetInitState, pver, MainNet, 25},
 		{msgInitState, msgInitState, pver, MainNet, 27},
 		{msgMixPR, msgMixPR, pver, MainNet, 167},
-		{msgMixKE, msgMixKE, pver, MainNet, 1449},
+		{msgMixKE, msgMixKE, pver, MainNet, 1453},
 		{msgMixCT, msgMixCT, pver, MainNet, 158},
 		{msgMixSR, msgMixSR, pver, MainNet, 161},
 		{msgMixFP, msgMixFP, pver, MainNet, 159},
diff --git a/wire/msgmixkeyexchange.go b/wire/msgmixkeyexchange.go
index 62c4553f16..938612ebab 100644
--- a/wire/msgmixkeyexchange.go
+++ b/wire/msgmixkeyexchange.go
@@ -32,6 +32,7 @@ type MsgMixKeyExchange struct {
 	SessionID  [32]byte
 	Epoch      uint64
 	Run        uint32
+	Pos        uint32
 	ECDH       [33]byte   // Secp256k1 public key
 	PQPK       [1218]byte // Sntrup4591761 public key
 	Commitment [32]byte
@@ -54,7 +55,7 @@ func (msg *MsgMixKeyExchange) BtcDecode(r io.Reader, pver uint32) error {
 	}
 
 	err := readElements(r, &msg.Signature, &msg.Identity, &msg.SessionID,
-		&msg.Epoch, &msg.Run, &msg.ECDH, &msg.PQPK, &msg.Commitment)
+		&msg.Epoch, &msg.Run, &msg.Pos, &msg.ECDH, &msg.PQPK, &msg.Commitment)
 	if err != nil {
 		return err
 	}
@@ -148,7 +149,7 @@ func (msg *MsgMixKeyExchange) writeMessageNoSignature(op string, w io.Writer, pv
 	}
 
 	err := writeElements(w, &msg.Identity, &msg.SessionID, msg.Epoch,
-		msg.Run, &msg.ECDH, &msg.PQPK, &msg.Commitment)
+		msg.Run, &msg.Pos, &msg.ECDH, &msg.PQPK, &msg.Commitment)
 	if err != nil {
 		return err
 	}
@@ -189,7 +190,7 @@ func (msg *MsgMixKeyExchange) MaxPayloadLength(pver uint32) uint32 {
 	}
 
 	// See tests for this calculation.
-	return 17811
+	return 17815
 }
 
 // Pub returns the message sender's public key identity.
@@ -221,7 +222,7 @@ func (msg *MsgMixKeyExchange) GetRun() uint32 {
 // Message interface using the passed parameters and defaults for the
 // remaining fields.
 func NewMsgMixKeyExchange(identity [33]byte, sid [32]byte, epoch uint64,
-	run uint32, ecdh [33]byte, pqpk [1218]byte, commitment [32]byte,
+	run uint32, pos uint32, ecdh [33]byte, pqpk [1218]byte, commitment [32]byte,
 	seenPRs []chainhash.Hash) *MsgMixKeyExchange {
 
 	return &MsgMixKeyExchange{
@@ -229,6 +230,7 @@ func NewMsgMixKeyExchange(identity [33]byte, sid [32]byte, epoch uint64,
 		SessionID:  sid,
 		Epoch:      epoch,
 		Run:        run,
+		Pos:        pos,
 		ECDH:       ecdh,
 		PQPK:       pqpk,
 		Commitment: commitment,
diff --git a/wire/msgmixkeyexchange_test.go b/wire/msgmixkeyexchange_test.go
index 94118c975a..4e62ea6df7 100644
--- a/wire/msgmixkeyexchange_test.go
+++ b/wire/msgmixkeyexchange_test.go
@@ -23,6 +23,7 @@ func newTestMixKeyExchange() *MsgMixKeyExchange {
 
 	const epoch = uint64(0x8383838383838383)
 	const run = uint32(0x84848484)
+	const pos = uint32(0x8C8C8C8C)
 
 	ecdh := *(*[33]byte)(repeat(0x85, 33))
 	pqpk := *(*[1218]byte)(repeat(0x86, 1218))
@@ -33,7 +34,7 @@ func newTestMixKeyExchange() *MsgMixKeyExchange {
 		copy(seenPRs[b-0x88][:], repeat(b, 32))
 	}
 
-	ke := NewMsgMixKeyExchange(id, sid, epoch, run, ecdh, pqpk, commitment, seenPRs)
+	ke := NewMsgMixKeyExchange(id, sid, epoch, run, pos, ecdh, pqpk, commitment, seenPRs)
 	ke.Signature = sig
 
 	return ke
@@ -56,6 +57,7 @@ func TestMsgMixKeyExchangeWire(t *testing.T) {
 	expected = append(expected, repeat(0x82, 32)...)   // Session ID
 	expected = append(expected, repeat(0x83, 8)...)    // Epoch
 	expected = append(expected, repeat(0x84, 4)...)    // Run
+	expected = append(expected, repeat(0x8c, 4)...)    // Unmixed position in session
 	expected = append(expected, repeat(0x85, 33)...)   // ECDH public key
 	expected = append(expected, repeat(0x86, 1218)...) // PQ public key
 	expected = append(expected, repeat(0x87, 32)...)   // Secrets commitment
@@ -159,6 +161,7 @@ func TestMsgMixKeyExchangeMaxPayloadLength(t *testing.T) {
 		32 + // Session ID
 		8 + // Epoch
 		4 + // Run
+		4 + // Unmixed position
 		33 + // ECDH public key
 		1218 + // sntrup4591761 public key
 		32 + // Secrets commitment