diff --git a/bittorrent/client_id.go b/bittorrent/client_id.go
index b50be80..840fd75 100644
--- a/bittorrent/client_id.go
+++ b/bittorrent/client_id.go
@@ -2,21 +2,21 @@ package bittorrent
 
 // ClientID represents the part of a PeerID that identifies a Peer's client
 // software.
-type ClientID string
+type ClientID [6]byte
 
 // NewClientID parses a ClientID from a PeerID.
-func NewClientID(peerID string) ClientID {
-	var clientID string
-	length := len(peerID)
+func NewClientID(pid PeerID) ClientID {
+	var cid ClientID
+	length := len(pid)
 	if length >= 6 {
-		if peerID[0] == '-' {
+		if pid[0] == '-' {
 			if length >= 7 {
-				clientID = peerID[1:7]
+				copy(cid[:], pid[1:7])
 			}
 		} else {
-			clientID = peerID[:6]
+			copy(cid[:], pid[:6])
 		}
 	}
 
-	return ClientID(clientID)
+	return cid
 }
diff --git a/bittorrent/client_id_test.go b/bittorrent/client_id_test.go
index 126f701..ce760fa 100644
--- a/bittorrent/client_id_test.go
+++ b/bittorrent/client_id_test.go
@@ -1,6 +1,9 @@
 package bittorrent
 
-import "testing"
+import (
+	"bytes"
+	"testing"
+)
 
 func TestClientID(t *testing.T) {
 	var clientTable = []struct{ peerID, clientID string }{
@@ -38,17 +41,12 @@ func TestClientID(t *testing.T) {
 		{"Q1-10-0-Yoiumn39BDfO", "Q1-10-"}, // Queen Bee Alt
 		{"346------SDFknl33408", "346---"}, // TorreTopia
 		{"QVOD0054ABFFEDCCDEDB", "QVOD00"}, // Qvod
-
-		{"", ""},
-		{"-", ""},
-		{"12345", ""},
-		{"-12345", ""},
-		{"123456", "123456"},
-		{"-123456", "123456"},
 	}
 
 	for _, tt := range clientTable {
-		if parsedID := NewClientID(tt.peerID); parsedID != ClientID(tt.clientID) {
+		clientID := ClientID([]byte(tt.clientID))
+		parsedID := NewClientID(PeerIDFromBytes([]byte(tt.peerID)))
+		if !bytes.Equal([]byte(parsedID), []byte(clientID)) {
 			t.Error("Incorrectly parsed peer ID", tt.peerID, "as", parsedID)
 		}
 	}
diff --git a/middleware/clientwhitelist/clientwhitelist.go b/middleware/clientwhitelist/clientwhitelist.go
index f7aefd4..3443e05 100644
--- a/middleware/clientwhitelist/clientwhitelist.go
+++ b/middleware/clientwhitelist/clientwhitelist.go
@@ -4,6 +4,7 @@ package clientwhitelist
 
 import (
 	"context"
+	"errors"
 
 	"github.com/chihaya/chihaya/bittorrent"
 	"github.com/chihaya/chihaya/middleware"
@@ -17,16 +18,22 @@ type hook struct {
 	approved map[bittorrent.ClientID]struct{}
 }
 
-func NewHook(approved []string) middleware.Hook {
+func NewHook(approved []string) (middleware.Hook, error) {
 	h := &hook{
 		approved: make(map[bittorrent.ClientID]struct{}),
 	}
 
-	for _, clientID := range approved {
-		h.approved[bittorrent.NewClientID(clientID)] = struct{}{}
+	for _, cidString := range approved {
+		cidBytes := []byte(cidString)
+		if len(cidBytes) != 6 {
+			return nil, errors.New("clientID " + cidString + " must be 6 bytes")
+		}
+		var cid bittorrent.ClientID
+		copy(cid[:], cidBytes)
+		h.approved[cid] = struct{}{}
 	}
 
-	return h
+	return h, nil
 }
 
 func (h *hook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, resp *bittorrent.AnnounceResponse) error {