diff --git a/client.go b/client.go
index 081f1259..435bc236 100644
--- a/client.go
+++ b/client.go
@@ -13,6 +13,7 @@ import (
 	"github.com/lucas-clemente/quic-go/internal/utils"
 	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/qerr"
+	"github.com/lucas-clemente/quic-go/wire"
 )
 
 type client struct {
@@ -224,7 +225,7 @@ func (c *client) handlePacket(remoteAddr net.Addr, packet []byte) {
 	rcvTime := time.Now()
 
 	r := bytes.NewReader(packet)
-	hdr, err := ParsePublicHeader(r, protocol.PerspectiveServer, c.version)
+	hdr, err := wire.ParsePublicHeader(r, protocol.PerspectiveServer, c.version)
 	if err != nil {
 		utils.Errorf("error parsing packet from %s: %s", remoteAddr.String(), err.Error())
 		// drop this packet if we can't parse the Public Header
@@ -280,7 +281,7 @@ func (c *client) handlePacket(remoteAddr net.Addr, packet []byte) {
 	})
 }
 
-func (c *client) handlePacketWithVersionFlag(hdr *PublicHeader) error {
+func (c *client) handlePacketWithVersionFlag(hdr *wire.PublicHeader) error {
 	for _, v := range hdr.SupportedVersions {
 		if v == c.version {
 			// the version negotiation packet contains the version that we offered
diff --git a/client_test.go b/client_test.go
index fc0271fb..ee8fc543 100644
--- a/client_test.go
+++ b/client_test.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/qerr"
+	"github.com/lucas-clemente/quic-go/wire"
 
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
@@ -228,7 +229,7 @@ var _ = Describe("Client", func() {
 
 		Context("version negotiation", func() {
 			It("recognizes that a packet without VersionFlag means that the server accepted the suggested version", func() {
-				ph := PublicHeader{
+				ph := wire.PublicHeader{
 					PacketNumber:    1,
 					PacketNumberLen: protocol.PacketNumberLen2,
 					ConnectionID:    0x1337,
@@ -262,7 +263,7 @@ var _ = Describe("Client", func() {
 				Expect(newVersion).ToNot(Equal(cl.version))
 				Expect(sess.packetCount).To(BeZero())
 				cl.connectionID = 0x1337
-				cl.handlePacket(nil, composeVersionNegotiation(0x1337, []protocol.VersionNumber{newVersion}))
+				cl.handlePacket(nil, wire.ComposeVersionNegotiation(0x1337, []protocol.VersionNumber{newVersion}))
 				Expect(cl.version).To(Equal(newVersion))
 				Expect(cl.versionNegotiated).To(BeTrue())
 				// it swapped the sessions
@@ -274,7 +275,7 @@ var _ = Describe("Client", func() {
 			})
 
 			It("errors if no matching version is found", func() {
-				cl.handlePacket(nil, composeVersionNegotiation(0x1337, []protocol.VersionNumber{1}))
+				cl.handlePacket(nil, wire.ComposeVersionNegotiation(0x1337, []protocol.VersionNumber{1}))
 				Expect(cl.session.(*mockSession).closed).To(BeTrue())
 				Expect(cl.session.(*mockSession).closeReason).To(MatchError(qerr.InvalidVersion))
 			})
@@ -283,13 +284,13 @@ var _ = Describe("Client", func() {
 				v := protocol.SupportedVersions[1]
 				Expect(v).ToNot(Equal(cl.version))
 				Expect(config.Versions).ToNot(ContainElement(v))
-				cl.handlePacket(nil, composeVersionNegotiation(0x1337, []protocol.VersionNumber{v}))
+				cl.handlePacket(nil, wire.ComposeVersionNegotiation(0x1337, []protocol.VersionNumber{v}))
 				Expect(cl.session.(*mockSession).closed).To(BeTrue())
 				Expect(cl.session.(*mockSession).closeReason).To(MatchError(qerr.InvalidVersion))
 			})
 
 			It("changes to the version preferred by the quic.Config", func() {
-				cl.handlePacket(nil, composeVersionNegotiation(0x1337, []protocol.VersionNumber{config.Versions[2], config.Versions[1]}))
+				cl.handlePacket(nil, wire.ComposeVersionNegotiation(0x1337, []protocol.VersionNumber{config.Versions[2], config.Versions[1]}))
 				Expect(cl.version).To(Equal(config.Versions[1]))
 			})
 
@@ -297,14 +298,14 @@ var _ = Describe("Client", func() {
 				// if the version was not yet negotiated, handlePacket would return a VersionNegotiationMismatch error, see above test
 				cl.versionNegotiated = true
 				Expect(sess.packetCount).To(BeZero())
-				cl.handlePacket(nil, composeVersionNegotiation(0x1337, []protocol.VersionNumber{1}))
+				cl.handlePacket(nil, wire.ComposeVersionNegotiation(0x1337, []protocol.VersionNumber{1}))
 				Expect(cl.versionNegotiated).To(BeTrue())
 				Expect(sess.packetCount).To(BeZero())
 			})
 
 			It("drops version negotiation packets that contain the offered version", func() {
 				ver := cl.version
-				cl.handlePacket(nil, composeVersionNegotiation(0x1337, []protocol.VersionNumber{ver}))
+				cl.handlePacket(nil, wire.ComposeVersionNegotiation(0x1337, []protocol.VersionNumber{ver}))
 				Expect(cl.version).To(Equal(ver))
 			})
 		})
@@ -351,7 +352,7 @@ var _ = Describe("Client", func() {
 
 	Context("handling packets", func() {
 		It("handles packets", func() {
-			ph := PublicHeader{
+			ph := wire.PublicHeader{
 				PacketNumber:    1,
 				PacketNumberLen: protocol.PacketNumberLen2,
 				ConnectionID:    0x1337,
diff --git a/integrationtests/tools/proxy/proxy.go b/integrationtests/tools/proxy/proxy.go
index bc72411d..77483a7a 100644
--- a/integrationtests/tools/proxy/proxy.go
+++ b/integrationtests/tools/proxy/proxy.go
@@ -7,8 +7,8 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/lucas-clemente/quic-go"
 	"github.com/lucas-clemente/quic-go/protocol"
+	"github.com/lucas-clemente/quic-go/wire"
 )
 
 // Connection is a UDP connection
@@ -165,7 +165,7 @@ func (p *QuicProxy) runProxy() error {
 		atomic.AddUint64(&conn.incomingPacketCounter, 1)
 
 		r := bytes.NewReader(raw)
-		hdr, err := quic.ParsePublicHeader(r, protocol.PerspectiveClient, protocol.VersionWhatever)
+		hdr, err := wire.ParsePublicHeader(r, protocol.PerspectiveClient, protocol.VersionWhatever)
 		if err != nil {
 			return err
 		}
@@ -202,7 +202,7 @@ func (p *QuicProxy) runConnection(conn *connection) error {
 
 		// TODO: Switch back to using the public header once Chrome properly sets the type byte.
 		// r := bytes.NewReader(raw)
-		// , err := quic.ParsePublicHeader(r, protocol.PerspectiveServer)
+		// , err := wire.ParsePublicHeader(r, protocol.PerspectiveServer)
 		// if err != nil {
 		// return err
 		// }
diff --git a/integrationtests/tools/proxy/proxy_test.go b/integrationtests/tools/proxy/proxy_test.go
index 565a8911..1ea73267 100644
--- a/integrationtests/tools/proxy/proxy_test.go
+++ b/integrationtests/tools/proxy/proxy_test.go
@@ -9,8 +9,8 @@ import (
 
 	"fmt"
 
-	"github.com/lucas-clemente/quic-go"
 	"github.com/lucas-clemente/quic-go/protocol"
+	"github.com/lucas-clemente/quic-go/wire"
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 )
@@ -22,7 +22,7 @@ var _ = Describe("QUIC Proxy", func() {
 
 	makePacket := func(p protocol.PacketNumber, payload []byte) []byte {
 		b := &bytes.Buffer{}
-		hdr := quic.PublicHeader{
+		hdr := wire.PublicHeader{
 			PacketNumber:         p,
 			PacketNumberLen:      protocol.PacketNumberLen6,
 			ConnectionID:         1337,
diff --git a/packet_packer.go b/packet_packer.go
index 050b93a7..addd11a3 100644
--- a/packet_packer.go
+++ b/packet_packer.go
@@ -264,10 +264,10 @@ func (p *packetPacker) QueueControlFrame(frame wire.Frame) {
 	}
 }
 
-func (p *packetPacker) getPublicHeader(encLevel protocol.EncryptionLevel) *PublicHeader {
+func (p *packetPacker) getPublicHeader(encLevel protocol.EncryptionLevel) *wire.PublicHeader {
 	pnum := p.packetNumberGenerator.Peek()
 	packetNumberLen := protocol.GetPacketNumberLengthForPublicHeader(pnum, p.leastUnacked)
-	publicHeader := &PublicHeader{
+	publicHeader := &wire.PublicHeader{
 		ConnectionID:         p.connectionID,
 		PacketNumber:         pnum,
 		PacketNumberLen:      packetNumberLen,
@@ -286,7 +286,7 @@ func (p *packetPacker) getPublicHeader(encLevel protocol.EncryptionLevel) *Publi
 }
 
 func (p *packetPacker) writeAndSealPacket(
-	publicHeader *PublicHeader,
+	publicHeader *wire.PublicHeader,
 	payloadFrames []wire.Frame,
 	sealer handshake.Sealer,
 ) ([]byte, error) {
diff --git a/packet_packer_test.go b/packet_packer_test.go
index 24e5de94..37421189 100644
--- a/packet_packer_test.go
+++ b/packet_packer_test.go
@@ -238,7 +238,7 @@ var _ = Describe("Packet packer", func() {
 		p, err := packer.PackPacket()
 		Expect(err).ToNot(HaveOccurred())
 		Expect(p).ToNot(BeNil())
-		hdr, err := ParsePublicHeader(bytes.NewReader(p.raw), protocol.PerspectiveClient, packer.version)
+		hdr, err := wire.ParsePublicHeader(bytes.NewReader(p.raw), protocol.PerspectiveClient, packer.version)
 		Expect(err).ToNot(HaveOccurred())
 		Expect(hdr.VersionFlag).To(BeTrue())
 		Expect(hdr.VersionNumber).To(Equal(packer.version))
@@ -252,7 +252,7 @@ var _ = Describe("Packet packer", func() {
 		p, err := packer.PackPacket()
 		Expect(err).ToNot(HaveOccurred())
 		Expect(p).ToNot(BeNil())
-		hdr, err := ParsePublicHeader(bytes.NewReader(p.raw), protocol.PerspectiveClient, packer.version)
+		hdr, err := wire.ParsePublicHeader(bytes.NewReader(p.raw), protocol.PerspectiveClient, packer.version)
 		Expect(err).ToNot(HaveOccurred())
 		Expect(hdr.VersionFlag).To(BeFalse())
 	})
diff --git a/packet_unpacker.go b/packet_unpacker.go
index 00ca7d19..8b5ba55d 100644
--- a/packet_unpacker.go
+++ b/packet_unpacker.go
@@ -24,7 +24,7 @@ type packetUnpacker struct {
 	aead    quicAEAD
 }
 
-func (u *packetUnpacker) Unpack(publicHeaderBinary []byte, hdr *PublicHeader, data []byte) (*unpackedPacket, error) {
+func (u *packetUnpacker) Unpack(publicHeaderBinary []byte, hdr *wire.PublicHeader, data []byte) (*unpackedPacket, error) {
 	buf := getPacketBuffer()
 	defer putPacketBuffer(buf)
 	decrypted, encryptionLevel, err := u.aead.Open(buf, data, hdr.PacketNumber, publicHeaderBinary)
diff --git a/packet_unpacker_test.go b/packet_unpacker_test.go
index 86856b1d..5426a2a3 100644
--- a/packet_unpacker_test.go
+++ b/packet_unpacker_test.go
@@ -31,14 +31,14 @@ var _ quicAEAD = &mockAEAD{}
 var _ = Describe("Packet unpacker", func() {
 	var (
 		unpacker *packetUnpacker
-		hdr      *PublicHeader
+		hdr      *wire.PublicHeader
 		hdrBin   []byte
 		data     []byte
 		buf      *bytes.Buffer
 	)
 
 	BeforeEach(func() {
-		hdr = &PublicHeader{
+		hdr = &wire.PublicHeader{
 			PacketNumber:    10,
 			PacketNumberLen: 1,
 		}
diff --git a/server.go b/server.go
index b45b760b..ea16ce59 100644
--- a/server.go
+++ b/server.go
@@ -13,6 +13,7 @@ import (
 	"github.com/lucas-clemente/quic-go/internal/utils"
 	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/qerr"
+	"github.com/lucas-clemente/quic-go/wire"
 )
 
 // packetHandler handles packets
@@ -212,7 +213,7 @@ func (s *server) handlePacket(pconn net.PacketConn, remoteAddr net.Addr, packet
 	rcvTime := time.Now()
 
 	r := bytes.NewReader(packet)
-	connID, err := peekConnectionID(r, protocol.PerspectiveClient)
+	connID, err := wire.PeekConnectionID(r, protocol.PerspectiveClient)
 	if err != nil {
 		return qerr.Error(qerr.InvalidPacketHeader, err.Error())
 	}
@@ -231,8 +232,8 @@ func (s *server) handlePacket(pconn net.PacketConn, remoteAddr net.Addr, packet
 		version = session.GetVersion()
 	}
 
-	hdr, err := ParsePublicHeader(r, protocol.PerspectiveClient, version)
-	if err == errPacketWithUnknownVersion {
+	hdr, err := wire.ParsePublicHeader(r, protocol.PerspectiveClient, version)
+	if err == wire.ErrPacketWithUnknownVersion {
 		_, err = pconn.WriteTo(writePublicReset(connID, 0, 0), remoteAddr)
 		return err
 	}
@@ -271,7 +272,7 @@ func (s *server) handlePacket(pconn net.PacketConn, remoteAddr net.Addr, packet
 			return errors.New("dropping small packet with unknown version")
 		}
 		utils.Infof("Client offered version %d, sending VersionNegotiationPacket", hdr.VersionNumber)
-		_, err = pconn.WriteTo(composeVersionNegotiation(hdr.ConnectionID, s.config.Versions), remoteAddr)
+		_, err = pconn.WriteTo(wire.ComposeVersionNegotiation(hdr.ConnectionID, s.config.Versions), remoteAddr)
 		return err
 	}
 
@@ -337,20 +338,3 @@ func (s *server) removeConnection(id protocol.ConnectionID) {
 		s.sessionsMutex.Unlock()
 	})
 }
-
-func composeVersionNegotiation(connectionID protocol.ConnectionID, versions []protocol.VersionNumber) []byte {
-	fullReply := &bytes.Buffer{}
-	responsePublicHeader := PublicHeader{
-		ConnectionID: connectionID,
-		PacketNumber: 1,
-		VersionFlag:  true,
-	}
-	err := responsePublicHeader.Write(fullReply, protocol.VersionWhatever, protocol.PerspectiveServer)
-	if err != nil {
-		utils.Errorf("error composing version negotiation packet: %s", err.Error())
-	}
-	for _, v := range versions {
-		utils.LittleEndian.WriteUint32(fullReply, protocol.VersionNumberToTag(v))
-	}
-	return fullReply.Bytes()
-}
diff --git a/server_test.go b/server_test.go
index bc26a2ec..b5c24155 100644
--- a/server_test.go
+++ b/server_test.go
@@ -14,6 +14,7 @@ import (
 	"github.com/lucas-clemente/quic-go/internal/utils"
 	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/qerr"
+	"github.com/lucas-clemente/quic-go/wire"
 
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
@@ -128,14 +129,6 @@ var _ = Describe("Server", func() {
 			Expect(serv.Addr().String()).To(Equal("192.168.13.37:1234"))
 		})
 
-		It("composes version negotiation packets", func() {
-			expected := append(
-				[]byte{0x01 | 0x08, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
-				[]byte{'Q', '0', '9', '9'}...,
-			)
-			Expect(composeVersionNegotiation(1, []protocol.VersionNumber{99})).To(Equal(expected))
-		})
-
 		It("creates new sessions", func() {
 			err := serv.handlePacket(nil, nil, firstPacket)
 			Expect(err).ToNot(HaveOccurred())
@@ -334,7 +327,7 @@ var _ = Describe("Server", func() {
 
 		It("doesn't respond with a version negotiation packet if the first packet is too small", func() {
 			b := &bytes.Buffer{}
-			hdr := PublicHeader{
+			hdr := wire.PublicHeader{
 				VersionFlag:     true,
 				ConnectionID:    0x1337,
 				PacketNumber:    1,
@@ -402,7 +395,7 @@ var _ = Describe("Server", func() {
 	It("setups and responds with version negotiation", func() {
 		config.Versions = []protocol.VersionNumber{99}
 		b := &bytes.Buffer{}
-		hdr := PublicHeader{
+		hdr := wire.PublicHeader{
 			VersionFlag:     true,
 			ConnectionID:    0x1337,
 			PacketNumber:    1,
diff --git a/session.go b/session.go
index a316c701..2111ec99 100644
--- a/session.go
+++ b/session.go
@@ -20,12 +20,12 @@ import (
 )
 
 type unpacker interface {
-	Unpack(publicHeaderBinary []byte, hdr *PublicHeader, data []byte) (*unpackedPacket, error)
+	Unpack(publicHeaderBinary []byte, hdr *wire.PublicHeader, data []byte) (*unpackedPacket, error)
 }
 
 type receivedPacket struct {
 	remoteAddr   net.Addr
-	publicHeader *PublicHeader
+	publicHeader *wire.PublicHeader
 	data         []byte
 	rcvTime      time.Time
 }
diff --git a/session_test.go b/session_test.go
index 09ac903c..759a6c62 100644
--- a/session_test.go
+++ b/session_test.go
@@ -61,7 +61,7 @@ type mockUnpacker struct {
 	unpackErr error
 }
 
-func (m *mockUnpacker) Unpack(publicHeaderBinary []byte, hdr *PublicHeader, data []byte) (*unpackedPacket, error) {
+func (m *mockUnpacker) Unpack(publicHeaderBinary []byte, hdr *wire.PublicHeader, data []byte) (*unpackedPacket, error) {
 	if m.unpackErr != nil {
 		return nil, m.unpackErr
 	}
@@ -847,11 +847,11 @@ var _ = Describe("Session", func() {
 	})
 
 	Context("receiving packets", func() {
-		var hdr *PublicHeader
+		var hdr *wire.PublicHeader
 
 		BeforeEach(func() {
 			sess.unpacker = &mockUnpacker{}
-			hdr = &PublicHeader{PacketNumberLen: protocol.PacketNumberLen6}
+			hdr = &wire.PublicHeader{PacketNumberLen: protocol.PacketNumberLen6}
 		})
 
 		It("sets the {last,largest}RcvdPacketNumber", func() {
@@ -903,7 +903,7 @@ var _ = Describe("Session", func() {
 				Expect(sess.conn.(*mockConnection).remoteAddr).ToNot(Equal(remoteIP))
 				p := receivedPacket{
 					remoteAddr:   remoteIP,
-					publicHeader: &PublicHeader{PacketNumber: 1337},
+					publicHeader: &wire.PublicHeader{PacketNumber: 1337},
 				}
 				err := sess.handlePacketImpl(&p)
 				Expect(err).ToNot(HaveOccurred())
@@ -919,7 +919,7 @@ var _ = Describe("Session", func() {
 				sess.unpacker.(*packetUnpacker).aead = &mockAEAD{}
 				p := receivedPacket{
 					remoteAddr:   attackerIP,
-					publicHeader: &PublicHeader{PacketNumber: 1337},
+					publicHeader: &wire.PublicHeader{PacketNumber: 1337},
 				}
 				err := sess.handlePacketImpl(&p)
 				quicErr := err.(*qerr.QuicError)
@@ -933,7 +933,7 @@ var _ = Describe("Session", func() {
 				Expect(sess.conn.(*mockConnection).remoteAddr).ToNot(Equal(remoteIP))
 				p := receivedPacket{
 					remoteAddr:   remoteIP,
-					publicHeader: &PublicHeader{PacketNumber: 1337},
+					publicHeader: &wire.PublicHeader{PacketNumber: 1337},
 				}
 				sess.unpacker.(*mockUnpacker).unpackErr = testErr
 				err := sess.handlePacketImpl(&p)
@@ -1347,7 +1347,7 @@ var _ = Describe("Session", func() {
 		// this completely fills up the undecryptable packets queue and triggers the public reset timer
 		sendUndecryptablePackets := func() {
 			for i := 0; i < protocol.MaxUndecryptablePackets+1; i++ {
-				hdr := &PublicHeader{
+				hdr := &wire.PublicHeader{
 					PacketNumber: protocol.PacketNumber(i + 1),
 				}
 				sess.handlePacket(&receivedPacket{
@@ -1420,7 +1420,7 @@ var _ = Describe("Session", func() {
 
 		It("unqueues undecryptable packets for later decryption", func() {
 			sess.undecryptablePackets = []*receivedPacket{{
-				publicHeader: &PublicHeader{PacketNumber: protocol.PacketNumber(42)},
+				publicHeader: &wire.PublicHeader{PacketNumber: protocol.PacketNumber(42)},
 			}}
 			Expect(sess.receivedPackets).NotTo(Receive())
 			sess.tryDecryptingQueuedPackets()
@@ -1722,10 +1722,10 @@ var _ = Describe("Client Session", func() {
 	})
 
 	Context("receiving packets", func() {
-		var hdr *PublicHeader
+		var hdr *wire.PublicHeader
 
 		BeforeEach(func() {
-			hdr = &PublicHeader{PacketNumberLen: protocol.PacketNumberLen6}
+			hdr = &wire.PublicHeader{PacketNumberLen: protocol.PacketNumberLen6}
 			sess.unpacker = &mockUnpacker{}
 		})
 
diff --git a/public_header.go b/wire/public_header.go
similarity index 91%
rename from public_header.go
rename to wire/public_header.go
index 9140fc8c..20fec06a 100644
--- a/public_header.go
+++ b/wire/public_header.go
@@ -1,4 +1,4 @@
-package quic
+package wire
 
 import (
 	"bytes"
@@ -11,13 +11,13 @@ import (
 )
 
 var (
-	errPacketNumberLenNotSet             = errors.New("PublicHeader: PacketNumberLen not set")
+	// ErrPacketWithUnknownVersion occurs when a packet with an unknown version is parsed.
+	// This can happen when the server is restarted. The client will send a packet without a version number.
+	ErrPacketWithUnknownVersion          = errors.New("PublicHeader: Received a packet without version number, that we don't know the version for")
 	errResetAndVersionFlagSet            = errors.New("PublicHeader: Reset Flag and Version Flag should not be set at the same time")
 	errReceivedTruncatedConnectionID     = qerr.Error(qerr.InvalidPacketHeader, "receiving packets with truncated ConnectionID is not supported")
 	errInvalidConnectionID               = qerr.Error(qerr.InvalidPacketHeader, "connection ID cannot be 0")
 	errGetLengthNotForVersionNegotiation = errors.New("PublicHeader: GetLength cannot be called for VersionNegotiation packets")
-	// this can happen when the server is restarted. The client will send a packet without a version number
-	errPacketWithUnknownVersion = errors.New("PublicHeader: Received a packet without version number, that we don't know the version for")
 )
 
 // The PublicHeader of a QUIC packet. Warning: This struct should not be considered stable and will change soon.
@@ -93,10 +93,6 @@ func (h *PublicHeader) Write(b *bytes.Buffer, version protocol.VersionNumber, pe
 		return nil
 	}
 
-	if h.PacketNumberLen != protocol.PacketNumberLen1 && h.PacketNumberLen != protocol.PacketNumberLen2 && h.PacketNumberLen != protocol.PacketNumberLen4 && h.PacketNumberLen != protocol.PacketNumberLen6 {
-		return errPacketNumberLenNotSet
-	}
-
 	switch h.PacketNumberLen {
 	case protocol.PacketNumberLen1:
 		b.WriteByte(uint8(h.PacketNumber))
@@ -107,15 +103,15 @@ func (h *PublicHeader) Write(b *bytes.Buffer, version protocol.VersionNumber, pe
 	case protocol.PacketNumberLen6:
 		utils.GetByteOrder(version).WriteUint48(b, uint64(h.PacketNumber)&(1<<48-1))
 	default:
-		return errPacketNumberLenNotSet
+		return errors.New("PublicHeader: PacketNumberLen not set")
 	}
 
 	return nil
 }
 
-// peekConnectionID parses the connection ID from a QUIC packet's public header.
+// PeekConnectionID parses the connection ID from a QUIC packet's public header.
 // If no error occurs, it restores the read position in the bytes.Reader.
-func peekConnectionID(b *bytes.Reader, packetSentBy protocol.Perspective) (protocol.ConnectionID, error) {
+func PeekConnectionID(b *bytes.Reader, packetSentBy protocol.Perspective) (protocol.ConnectionID, error) {
 	var connectionID protocol.ConnectionID
 	publicFlagByte, err := b.ReadByte()
 	if err != nil {
@@ -156,7 +152,7 @@ func ParsePublicHeader(b *bytes.Reader, packetSentBy protocol.Perspective, versi
 	header.ResetFlag = publicFlagByte&0x02 > 0
 	header.VersionFlag = publicFlagByte&0x01 > 0
 	if version == protocol.VersionUnknown && !(header.VersionFlag || header.ResetFlag) {
-		return nil, errPacketWithUnknownVersion
+		return nil, ErrPacketWithUnknownVersion
 	}
 
 	// TODO: activate this check once Chrome sends the correct value
diff --git a/public_header_test.go b/wire/public_header_test.go
similarity index 97%
rename from public_header_test.go
rename to wire/public_header_test.go
index 6d151234..fbad6919 100644
--- a/public_header_test.go
+++ b/wire/public_header_test.go
@@ -1,4 +1,4 @@
-package quic
+package wire
 
 import (
 	"bytes"
@@ -15,14 +15,14 @@ var _ = Describe("Public Header", func() {
 	Context("parsing the connection ID", func() {
 		It("does not accept truncated connection ID as a server", func() {
 			b := bytes.NewReader([]byte{0x00, 0x01})
-			_, err := peekConnectionID(b, protocol.PerspectiveClient)
+			_, err := PeekConnectionID(b, protocol.PerspectiveClient)
 			Expect(err).To(MatchError(errReceivedTruncatedConnectionID))
 		})
 
 		It("gets the connection ID", func() {
 			b := bytes.NewReader([]byte{0x09, 0xf6, 0x19, 0x86, 0x66, 0x9b, 0x9f, 0xfa, 0x4c, 0x51, 0x30, 0x33, 0x34, 0x01})
 			len := b.Len()
-			connID, err := peekConnectionID(b, protocol.PerspectiveClient)
+			connID, err := PeekConnectionID(b, protocol.PerspectiveClient)
 			Expect(err).ToNot(HaveOccurred())
 			Expect(connID).To(Equal(protocol.ConnectionID(0x4cfa9f9b668619f6)))
 			Expect(b.Len()).To(Equal(len))
@@ -30,20 +30,20 @@ var _ = Describe("Public Header", func() {
 
 		It("errors if the Public Header is too short", func() {
 			b := bytes.NewReader([]byte{0x09, 0xf6, 0x19, 0x86, 0x66, 0x9b})
-			_, err := peekConnectionID(b, protocol.PerspectiveClient)
+			_, err := PeekConnectionID(b, protocol.PerspectiveClient)
 			Expect(err).To(HaveOccurred())
 		})
 
 		It("errors if the Public Header is empty", func() {
 			b := bytes.NewReader([]byte{})
-			_, err := peekConnectionID(b, protocol.PerspectiveClient)
+			_, err := PeekConnectionID(b, protocol.PerspectiveClient)
 			Expect(err).To(HaveOccurred())
 		})
 
 		It("accepts a truncated connection ID as a client", func() {
 			b := bytes.NewReader([]byte{0x00, 0x01})
 			len := b.Len()
-			connID, err := peekConnectionID(b, protocol.PerspectiveServer)
+			connID, err := PeekConnectionID(b, protocol.PerspectiveServer)
 			Expect(err).ToNot(HaveOccurred())
 			Expect(connID).To(BeZero())
 			Expect(b.Len()).To(Equal(len))
@@ -116,7 +116,7 @@ var _ = Describe("Public Header", func() {
 		It("returns an unknown version error when receiving a packet without a version for which the version is not given", func() {
 			b := bytes.NewReader([]byte{0x10, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0xef})
 			_, err := ParsePublicHeader(b, protocol.PerspectiveServer, protocol.VersionUnknown)
-			Expect(err).To(MatchError(errPacketWithUnknownVersion))
+			Expect(err).To(MatchError(ErrPacketWithUnknownVersion))
 		})
 
 		PIt("rejects diversification nonces sent by the client", func() {
@@ -136,7 +136,7 @@ var _ = Describe("Public Header", func() {
 			}
 
 			It("parses version negotiation packets sent by the server", func() {
-				b := bytes.NewReader(composeVersionNegotiation(0x1337, protocol.SupportedVersions))
+				b := bytes.NewReader(ComposeVersionNegotiation(0x1337, protocol.SupportedVersions))
 				hdr, err := ParsePublicHeader(b, protocol.PerspectiveServer, protocol.VersionUnknown)
 				Expect(err).ToNot(HaveOccurred())
 				Expect(hdr.VersionFlag).To(BeTrue())
@@ -169,7 +169,7 @@ var _ = Describe("Public Header", func() {
 			})
 
 			It("errors on invalid version tags", func() {
-				data := composeVersionNegotiation(0x1337, protocol.SupportedVersions)
+				data := ComposeVersionNegotiation(0x1337, protocol.SupportedVersions)
 				data = append(data, []byte{0x13, 0x37}...)
 				b := bytes.NewReader(data)
 				_, err := ParsePublicHeader(b, protocol.PerspectiveServer, protocol.VersionUnknown)
@@ -300,7 +300,7 @@ var _ = Describe("Public Header", func() {
 			}
 			b := &bytes.Buffer{}
 			err := hdr.Write(b, protocol.VersionWhatever, protocol.PerspectiveServer)
-			Expect(err).To(MatchError(errPacketNumberLenNotSet))
+			Expect(err).To(MatchError("PublicHeader: PacketNumberLen not set"))
 		})
 
 		It("truncates the connection ID", func() {
@@ -526,7 +526,7 @@ var _ = Describe("Public Header", func() {
 					PacketNumber: 0xDECAFBAD,
 				}
 				err := hdr.Write(b, protocol.VersionWhatever, protocol.PerspectiveServer)
-				Expect(err).To(MatchError(errPacketNumberLenNotSet))
+				Expect(err).To(MatchError("PublicHeader: PacketNumberLen not set"))
 			})
 
 			Context("in little endian", func() {
diff --git a/wire/version_negotiation.go b/wire/version_negotiation.go
new file mode 100644
index 00000000..7d3f6f23
--- /dev/null
+++ b/wire/version_negotiation.go
@@ -0,0 +1,26 @@
+package wire
+
+import (
+	"bytes"
+
+	"github.com/lucas-clemente/quic-go/internal/utils"
+	"github.com/lucas-clemente/quic-go/protocol"
+)
+
+// ComposeVersionNegotiation composes a Version Negotiation Packet
+func ComposeVersionNegotiation(connectionID protocol.ConnectionID, versions []protocol.VersionNumber) []byte {
+	fullReply := &bytes.Buffer{}
+	responsePublicHeader := PublicHeader{
+		ConnectionID: connectionID,
+		PacketNumber: 1,
+		VersionFlag:  true,
+	}
+	err := responsePublicHeader.Write(fullReply, protocol.VersionWhatever, protocol.PerspectiveServer)
+	if err != nil {
+		utils.Errorf("error composing version negotiation packet: %s", err.Error())
+	}
+	for _, v := range versions {
+		utils.LittleEndian.WriteUint32(fullReply, protocol.VersionNumberToTag(v))
+	}
+	return fullReply.Bytes()
+}
diff --git a/wire/version_negotiation_test.go b/wire/version_negotiation_test.go
new file mode 100644
index 00000000..172d78e3
--- /dev/null
+++ b/wire/version_negotiation_test.go
@@ -0,0 +1,17 @@
+package wire
+
+import (
+	"github.com/lucas-clemente/quic-go/protocol"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Version Negotiation Packet", func() {
+	It("composes version negotiation packets", func() {
+		expected := append(
+			[]byte{0x01 | 0x08, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0},
+			[]byte{'Q', '0', '9', '9'}...,
+		)
+		Expect(ComposeVersionNegotiation(1, []protocol.VersionNumber{99})).To(Equal(expected))
+	})
+})