diff --git a/session/handler.go b/session/handler.go
index 0dc6c53..4bea5b5 100644
--- a/session/handler.go
+++ b/session/handler.go
@@ -5,7 +5,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"slices"
 	"time"
 
 	packet2 "github.com/cooldogedev/spectrum/server/packet"
@@ -142,7 +141,7 @@ func handleClientPacket(s *Session, header *packet.Header, pool packet.Pool, shi
 		return errors.New("failed to decode header")
 	}
 
-	if !slices.Contains(s.opts.ClientDecode, header.PacketID) {
+	if _, ok := s.clientDecode[header.PacketID]; !ok {
 		s.processor.ProcessClientEncoded(ctx, &payload)
 		if !ctx.Cancelled() {
 			return s.Server().Write(payload)
diff --git a/session/session.go b/session/session.go
index 1777817..70675a6 100644
--- a/session/session.go
+++ b/session/session.go
@@ -44,6 +44,8 @@ type Session struct {
 	latency      atomic.Int64
 	transferring atomic.Bool
 	once         sync.Once
+
+	clientDecode map[uint32]struct{}
 }
 
 // NewSession creates a new Session instance using the provided minecraft.Conn.
@@ -61,6 +63,8 @@ func NewSession(client *minecraft.Conn, logger *slog.Logger, registry *Registry,
 		animation: &animation.Dimension{},
 		processor: NopProcessor{},
 		tracker:   newTracker(),
+
+		clientDecode: opts.ClientDecodeAsMap(),
 	}
 	s.ctx, s.cancelFunc = context.WithCancelCause(client.Context())
 	return s
@@ -234,6 +238,7 @@ func (s *Session) Opts() util.Opts {
 // SetOpts updates the session options.
 func (s *Session) SetOpts(opts util.Opts) {
 	s.opts = opts
+	s.clientDecode = opts.ClientDecodeAsMap()
 }
 
 // Processor returns the current processor.
diff --git a/util/opts.go b/util/opts.go
index 641fc34..fc88702 100644
--- a/util/opts.go
+++ b/util/opts.go
@@ -21,6 +21,15 @@ type Opts struct {
 	Token string `yaml:"token"`
 }
 
+// ClientDecodeAsMap converts the ClientDecode slice to a map for faster lookups.
+func (opts *Opts) ClientDecodeAsMap() map[uint32]struct{} {
+	m := make(map[uint32]struct{}, len(opts.ClientDecode))
+	for _, id := range opts.ClientDecode {
+		m[id] = struct{}{}
+	}
+	return m
+}
+
 // DefaultOpts returns the default configuration options for Spectrum.
 func DefaultOpts() *Opts {
 	return &Opts{