diff --git a/crypto/AEAD.go b/crypto/AEAD.go
index c7169792..df7d7b4a 100644
--- a/crypto/AEAD.go
+++ b/crypto/AEAD.go
@@ -3,10 +3,12 @@ package crypto
 import (
 	"bytes"
 	"io"
+
+	"github.com/lucas-clemente/quic-go/protocol"
 )
 
 // An AEAD implements QUIC's authenticated encryption and associated data
 type AEAD interface {
-	Open(packetNumber uint64, associatedData []byte, ciphertext io.Reader) (*bytes.Reader, error)
-	Seal(packetNumber uint64, b *bytes.Buffer, associatedData []byte, plaintext []byte)
+	Open(packetNumber protocol.PacketNumber, associatedData []byte, ciphertext io.Reader) (*bytes.Reader, error)
+	Seal(packetNumber protocol.PacketNumber, b *bytes.Buffer, associatedData []byte, plaintext []byte)
 }
diff --git a/crypto/NullAEAD.go b/crypto/NullAEAD.go
index 92df9494..42608e59 100644
--- a/crypto/NullAEAD.go
+++ b/crypto/NullAEAD.go
@@ -7,6 +7,7 @@ import (
 	"io"
 	"io/ioutil"
 
+	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/utils"
 )
 
@@ -16,7 +17,7 @@ type NullAEAD struct{}
 var _ AEAD = &NullAEAD{}
 
 // Open and verify the ciphertext
-func (*NullAEAD) Open(packetNumber uint64, associatedData []byte, r io.Reader) (*bytes.Reader, error) {
+func (*NullAEAD) Open(packetNumber protocol.PacketNumber, associatedData []byte, r io.Reader) (*bytes.Reader, error) {
 	ciphertext, err := ioutil.ReadAll(r)
 	if err != nil {
 		return nil, err
@@ -40,7 +41,7 @@ func (*NullAEAD) Open(packetNumber uint64, associatedData []byte, r io.Reader) (
 }
 
 // Seal writes hash and ciphertext to the buffer
-func (*NullAEAD) Seal(packetNumber uint64, b *bytes.Buffer, associatedData []byte, plaintext []byte) {
+func (*NullAEAD) Seal(packetNumber protocol.PacketNumber, b *bytes.Buffer, associatedData []byte, plaintext []byte) {
 	hash := New128a()
 	hash.Write(associatedData)
 	hash.Write(plaintext)
diff --git a/crypto/aes_gcm_aead.go b/crypto/aes_gcm_aead.go
index 1d5973bb..3082fcf2 100644
--- a/crypto/aes_gcm_aead.go
+++ b/crypto/aes_gcm_aead.go
@@ -8,6 +8,8 @@ import (
 	"errors"
 	"io"
 	"io/ioutil"
+
+	"github.com/lucas-clemente/quic-go/protocol"
 )
 
 type aeadAESGCM struct {
@@ -46,7 +48,7 @@ func NewAEADAESGCM(otherKey []byte, myKey []byte, otherIV []byte, myIV []byte) (
 	}, nil
 }
 
-func (aead *aeadAESGCM) Open(packetNumber uint64, associatedData []byte, r io.Reader) (*bytes.Reader, error) {
+func (aead *aeadAESGCM) Open(packetNumber protocol.PacketNumber, associatedData []byte, r io.Reader) (*bytes.Reader, error) {
 	ciphertext, err := ioutil.ReadAll(r)
 	if err != nil {
 		return nil, err
@@ -58,14 +60,14 @@ func (aead *aeadAESGCM) Open(packetNumber uint64, associatedData []byte, r io.Re
 	return bytes.NewReader(plaintext), nil
 }
 
-func (aead *aeadAESGCM) Seal(packetNumber uint64, b *bytes.Buffer, associatedData []byte, plaintext []byte) {
+func (aead *aeadAESGCM) Seal(packetNumber protocol.PacketNumber, b *bytes.Buffer, associatedData []byte, plaintext []byte) {
 	ciphertext := aead.encrypter.Seal(nil, makeNonce(aead.myIV, packetNumber), plaintext, associatedData)
 	b.Write(ciphertext)
 }
 
-func makeNonce(iv []byte, packetNumber uint64) []byte {
+func makeNonce(iv []byte, packetNumber protocol.PacketNumber) []byte {
 	res := make([]byte, 12)
 	copy(res[0:4], iv)
-	binary.LittleEndian.PutUint64(res[4:12], packetNumber)
+	binary.LittleEndian.PutUint64(res[4:12], uint64(packetNumber))
 	return res
 }
diff --git a/entropy_accumulator.go b/entropy_accumulator.go
index cfa2fbdc..14594eef 100644
--- a/entropy_accumulator.go
+++ b/entropy_accumulator.go
@@ -1,10 +1,12 @@
 package quic
 
+import "github.com/lucas-clemente/quic-go/protocol"
+
 // EntropyAccumulator accumulates the entropy according to the QUIC docs
 type EntropyAccumulator byte
 
 // Add the contribution of the entropy flag of a given packet number
-func (e *EntropyAccumulator) Add(packetNumber uint64, entropyFlag bool) {
+func (e *EntropyAccumulator) Add(packetNumber protocol.PacketNumber, entropyFlag bool) {
 	if entropyFlag {
 		(*e) ^= 0x01 << (packetNumber % 8)
 	}
diff --git a/protocol/protocol.go b/protocol/protocol.go
new file mode 100644
index 00000000..e869b8be
--- /dev/null
+++ b/protocol/protocol.go
@@ -0,0 +1,4 @@
+package protocol
+
+// A PacketNumber in QUIC
+type PacketNumber uint64
diff --git a/public_header.go b/public_header.go
index a77152ac..1a994c15 100644
--- a/public_header.go
+++ b/public_header.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"io"
 
+	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/utils"
 )
 
@@ -14,7 +15,7 @@ type PublicHeader struct {
 	ResetFlag    bool
 	ConnectionID uint64
 	QuicVersion  uint32
-	PacketNumber uint64
+	PacketNumber protocol.PacketNumber
 	// packetNumberLen uint8
 }
 
@@ -85,10 +86,11 @@ func ParsePublicHeader(b io.ByteReader) (*PublicHeader, error) {
 	}
 
 	// Packet number
-	header.PacketNumber, err = utils.ReadUintN(b, packetNumberLen)
+	pcktNumber, err := utils.ReadUintN(b, packetNumberLen)
 	if err != nil {
 		return nil, err
 	}
+	header.PacketNumber = protocol.PacketNumber(pcktNumber)
 
 	return header, nil
 }
diff --git a/public_header_test.go b/public_header_test.go
index f5f6399f..0172eebf 100644
--- a/public_header_test.go
+++ b/public_header_test.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 
+	"github.com/lucas-clemente/quic-go/protocol"
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 )
@@ -18,7 +19,7 @@ var _ = Describe("Public Header", func() {
 			Expect(publicHeader.ResetFlag).To(BeFalse())
 			Expect(publicHeader.ConnectionID).To(Equal(uint64(0x4cfa9f9b668619f6)))
 			Expect(publicHeader.QuicVersion).To(Equal(binary.BigEndian.Uint32([]byte("Q030"))))
-			Expect(publicHeader.PacketNumber).To(Equal(uint64(1)))
+			Expect(publicHeader.PacketNumber).To(Equal(protocol.PacketNumber(1)))
 			Expect(b.Len()).To(BeZero())
 		})
 
@@ -52,7 +53,7 @@ var _ = Describe("Public Header", func() {
 			b := bytes.NewReader([]byte{0x10, 0xde, 0xca})
 			publicHeader, err := ParsePublicHeader(b)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(publicHeader.PacketNumber).To(Equal(uint64(0xcade)))
+			Expect(publicHeader.PacketNumber).To(Equal(protocol.PacketNumber(0xcade)))
 			Expect(b.Len()).To(BeZero())
 		})
 
@@ -60,7 +61,7 @@ var _ = Describe("Public Header", func() {
 			b := bytes.NewReader([]byte{0x20, 0xad, 0xfb, 0xca, 0xde})
 			publicHeader, err := ParsePublicHeader(b)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(publicHeader.PacketNumber).To(Equal(uint64(0xdecafbad)))
+			Expect(publicHeader.PacketNumber).To(Equal(protocol.PacketNumber(0xdecafbad)))
 			Expect(b.Len()).To(BeZero())
 		})
 
@@ -68,7 +69,7 @@ var _ = Describe("Public Header", func() {
 			b := bytes.NewReader([]byte{0x30, 0x23, 0x42, 0xad, 0xfb, 0xca, 0xde})
 			publicHeader, err := ParsePublicHeader(b)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(publicHeader.PacketNumber).To(Equal(uint64(0xdecafbad4223)))
+			Expect(publicHeader.PacketNumber).To(Equal(protocol.PacketNumber(0xdecafbad4223)))
 			Expect(b.Len()).To(BeZero())
 		})
 	})