diff --git a/examples/main.go b/examples/main.go
index 3133163..5adae8c 100644
--- a/examples/main.go
+++ b/examples/main.go
@@ -44,7 +44,8 @@ func main() {
 	}
 
 	// 4. Encode the .trix container into its binary format
-	encodedTrix, err := trix.Encode(trixContainer)
+	magicNumber := "MyT1" // My Trix 1
+	encodedTrix, err := trix.Encode(trixContainer, magicNumber)
 	if err != nil {
 		log.Fatalf("Failed to encode .trix container: %v", err)
 	}
@@ -52,7 +53,7 @@ func main() {
 	fmt.Println("Successfully created .trix container.")
 
 	// 5. Decode the .trix container to retrieve the encrypted data
-	decodedTrix, err := trix.Decode(encodedTrix)
+	decodedTrix, err := trix.Decode(encodedTrix, magicNumber)
 	if err != nil {
 		log.Fatalf("Failed to decode .trix container: %v", err)
 	}
diff --git a/pkg/trix/trix.go b/pkg/trix/trix.go
index 575b55e..8f1c9e7 100644
--- a/pkg/trix/trix.go
+++ b/pkg/trix/trix.go
@@ -5,17 +5,18 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 )
 
 const (
-	MagicNumber = "TRIX"
-	Version     = 2
+	Version = 2
 )
 
 var (
 	ErrInvalidMagicNumber = errors.New("trix: invalid magic number")
 	ErrInvalidVersion     = errors.New("trix: invalid version")
+	ErrMagicNumberLength  = errors.New("trix: magic number must be 4 bytes long")
 )
 
 // Trix represents the structure of a .trix file.
@@ -25,7 +26,11 @@ type Trix struct {
 }
 
 // Encode serializes a Trix struct into the .trix binary format.
-func Encode(trix *Trix) ([]byte, error) {
+func Encode(trix *Trix, magicNumber string) ([]byte, error) {
+	if len(magicNumber) != 4 {
+		return nil, ErrMagicNumberLength
+	}
+
 	headerBytes, err := json.Marshal(trix.Header)
 	if err != nil {
 		return nil, err
@@ -35,7 +40,7 @@ func Encode(trix *Trix) ([]byte, error) {
 	buf := new(bytes.Buffer)
 
 	// Write Magic Number
-	if _, err := buf.WriteString(MagicNumber); err != nil {
+	if _, err := buf.WriteString(magicNumber); err != nil {
 		return nil, err
 	}
 
@@ -63,7 +68,11 @@ func Encode(trix *Trix) ([]byte, error) {
 }
 
 // Decode deserializes the .trix binary format into a Trix struct.
-func Decode(data []byte) (*Trix, error) {
+func Decode(data []byte, magicNumber string) (*Trix, error) {
+	if len(magicNumber) != 4 {
+		return nil, ErrMagicNumberLength
+	}
+
 	buf := bytes.NewReader(data)
 
 	// Read and Verify Magic Number
@@ -71,8 +80,8 @@ func Decode(data []byte) (*Trix, error) {
 	if _, err := io.ReadFull(buf, magic); err != nil {
 		return nil, err
 	}
-	if string(magic) != MagicNumber {
-		return nil, ErrInvalidMagicNumber
+	if string(magic) != magicNumber {
+		return nil, fmt.Errorf("%w: expected %s, got %s", ErrInvalidMagicNumber, magicNumber, string(magic))
 	}
 
 	// Read and Verify Version
diff --git a/pkg/trix/trix_test.go b/pkg/trix/trix_test.go
index d46695f..13531e7 100644
--- a/pkg/trix/trix_test.go
+++ b/pkg/trix/trix_test.go
@@ -21,12 +21,72 @@ func TestEncodeDecode(t *testing.T) {
 		Payload: payload,
 	}
 
-	encoded, err := Encode(trix)
+	magicNumber := "TRIX"
+	encoded, err := Encode(trix, magicNumber)
 	assert.NoError(t, err)
 
-	decoded, err := Decode(encoded)
+	decoded, err := Decode(encoded, magicNumber)
 	assert.NoError(t, err)
 
 	assert.True(t, reflect.DeepEqual(trix.Header, decoded.Header))
 	assert.Equal(t, trix.Payload, decoded.Payload)
 }
+
+func TestEncodeDecode_InvalidMagicNumber(t *testing.T) {
+	header := map[string]interface{}{
+		"content_type": "application/octet-stream",
+	}
+	payload := []byte("This is a secret message.")
+
+	trix := &Trix{
+		Header:  header,
+		Payload: payload,
+	}
+
+	magicNumber := "TRIX"
+	wrongMagicNumber := "XXXX"
+	encoded, err := Encode(trix, magicNumber)
+	assert.NoError(t, err)
+
+	_, err = Decode(encoded, wrongMagicNumber)
+	assert.Error(t, err)
+	assert.EqualError(t, err, "trix: invalid magic number: expected XXXX, got TRIX")
+}
+
+func TestEncode_InvalidMagicNumberLength(t *testing.T) {
+	header := map[string]interface{}{
+		"content_type": "application/octet-stream",
+	}
+	payload := []byte("This is a secret message.")
+
+	trix := &Trix{
+		Header:  header,
+		Payload: payload,
+	}
+
+	magicNumber := "TOOLONG"
+	_, err := Encode(trix, magicNumber)
+	assert.Error(t, err)
+	assert.EqualError(t, err, "trix: magic number must be 4 bytes long")
+}
+
+func TestDecode_InvalidMagicNumberLength(t *testing.T) {
+	header := map[string]interface{}{
+		"content_type": "application/octet-stream",
+	}
+	payload := []byte("This is a secret message.")
+
+	trix := &Trix{
+		Header:  header,
+		Payload: payload,
+	}
+
+	magicNumber := "TRIX"
+	encoded, err := Encode(trix, magicNumber)
+	assert.NoError(t, err)
+
+	invalidMagicNumber := "SHORT"
+	_, err = Decode(encoded, invalidMagicNumber)
+	assert.Error(t, err)
+	assert.EqualError(t, err, "trix: magic number must be 4 bytes long")
+}