diff --git a/integrationtests/self/mitm_test.go b/integrationtests/self/mitm_test.go
index 2025c2a3..8f941564 100644
--- a/integrationtests/self/mitm_test.go
+++ b/integrationtests/self/mitm_test.go
@@ -418,18 +418,15 @@ var _ = Describe("MITM test", func() {
 
 				// client connection closes immediately on receiving ack for unsent packet
 				It("fails when a forged initial packet with ack for unsent packet is sent to client", func() {
+					clientAddr := clientConn.LocalAddr()
 					delayCb := func(dir quicproxy.Direction, raw []byte) time.Duration {
 						if dir == quicproxy.DirectionIncoming {
-							defer GinkgoRecover()
-
 							hdr, _, _, err := wire.ParsePacket(raw, connIDLen)
 							Expect(err).ToNot(HaveOccurred())
-
 							if hdr.Type != protocol.PacketTypeInitial {
 								return 0
 							}
-
-							sendForgedInitialPacketWithAck(serverConn, clientConn.LocalAddr(), hdr)
+							sendForgedInitialPacketWithAck(serverConn, clientAddr, hdr)
 						}
 						return rtt
 					}
@@ -439,7 +436,6 @@ var _ = Describe("MITM test", func() {
 					Expect(err.(*qerr.QuicError).ErrorCode).To(Equal(qerr.ProtocolViolation))
 					Expect(err.Error()).To(ContainSubstring("Received ACK for an unsent packet"))
 				})
-
 			})
 		})
 	}
diff --git a/integrationtests/tools/proxy/proxy.go b/integrationtests/tools/proxy/proxy.go
index 1c1d224a..1e5c90ec 100644
--- a/integrationtests/tools/proxy/proxy.go
+++ b/integrationtests/tools/proxy/proxy.go
@@ -2,6 +2,7 @@ package quicproxy
 
 import (
 	"net"
+	"sort"
 	"sync"
 	"time"
 
@@ -13,6 +14,15 @@ import (
 type connection struct {
 	ClientAddr *net.UDPAddr // Address of the client
 	ServerConn *net.UDPConn // UDP connection to server
+
+	incomingPackets chan packetEntry
+
+	Incoming *queue
+	Outgoing *queue
+}
+
+func (c *connection) queuePacket(t time.Time, b []byte) {
+	c.incomingPackets <- packetEntry{Time: t, Raw: b}
 }
 
 // Direction is the direction a packet is sent.
@@ -27,12 +37,63 @@ const (
 	DirectionBoth
 )
 
+type packetEntry struct {
+	Time time.Time
+	Raw  []byte
+}
+
+type packetEntries []packetEntry
+
+func (e packetEntries) Len() int           { return len(e) }
+func (e packetEntries) Less(i, j int) bool { return e[i].Time.Before(e[j].Time) }
+func (e packetEntries) Swap(i, j int)      { e[i], e[j] = e[j], e[i] }
+
+type queue struct {
+	sync.Mutex
+
+	timer   *utils.Timer
+	Packets packetEntries
+}
+
+func newQueue() *queue {
+	return &queue{timer: utils.NewTimer()}
+}
+
+func (q *queue) Add(e packetEntry) {
+	q.Lock()
+	q.Packets = append(q.Packets, e)
+	if len(q.Packets) > 1 {
+		lastIndex := len(q.Packets) - 1
+		if q.Packets[lastIndex].Time.Before(q.Packets[lastIndex-1].Time) {
+			sort.Stable(q.Packets)
+		}
+	}
+	q.timer.Reset(q.Packets[0].Time)
+	q.Unlock()
+}
+
+func (q *queue) Get() []byte {
+	q.Lock()
+	raw := q.Packets[0].Raw
+	q.Packets = q.Packets[1:]
+	if len(q.Packets) > 0 {
+		q.timer.Reset(q.Packets[0].Time)
+	}
+	q.Unlock()
+	return raw
+}
+
+func (q *queue) Timer() <-chan time.Time { return q.timer.Chan() }
+func (q *queue) SetTimerRead()           { q.timer.SetRead() }
+
+func (q *queue) Close() { q.timer.Stop() }
+
 func (d Direction) String() string {
 	switch d {
 	case DirectionIncoming:
-		return "incoming"
+		return "Incoming"
 	case DirectionOutgoing:
-		return "outgoing"
+		return "Outgoing"
 	case DirectionBoth:
 		return "both"
 	default:
@@ -81,15 +142,14 @@ type Opts struct {
 type QuicProxy struct {
 	mutex sync.Mutex
 
+	closeChan chan struct{}
+
 	conn       *net.UDPConn
 	serverAddr *net.UDPAddr
 
 	dropPacket  DropCallback
 	delayPacket DelayCallback
 
-	timerID uint64
-	timers  map[uint64]*time.Timer
-
 	// Mapping from client addresses (as host:port) to connection
 	clientDict map[string]*connection
 
@@ -127,10 +187,10 @@ func NewQuicProxy(local string, opts *Opts) (*QuicProxy, error) {
 	p := QuicProxy{
 		clientDict:  make(map[string]*connection),
 		conn:        conn,
+		closeChan:   make(chan struct{}),
 		serverAddr:  raddr,
 		dropPacket:  packetDropper,
 		delayPacket: packetDelayer,
-		timers:      make(map[uint64]*time.Timer),
 		logger:      utils.DefaultLogger.WithPrefix("proxy"),
 	}
 
@@ -143,13 +203,13 @@ func NewQuicProxy(local string, opts *Opts) (*QuicProxy, error) {
 func (p *QuicProxy) Close() error {
 	p.mutex.Lock()
 	defer p.mutex.Unlock()
+	close(p.closeChan)
 	for _, c := range p.clientDict {
 		if err := c.ServerConn.Close(); err != nil {
 			return err
 		}
-	}
-	for _, t := range p.timers {
-		t.Stop()
+		c.Incoming.Close()
+		c.Outgoing.Close()
 	}
 	return p.conn.Close()
 }
@@ -170,8 +230,11 @@ func (p *QuicProxy) newConnection(cliAddr *net.UDPAddr) (*connection, error) {
 		return nil, err
 	}
 	return &connection{
-		ClientAddr: cliAddr,
-		ServerConn: srvudp,
+		ClientAddr:      cliAddr,
+		ServerConn:      srvudp,
+		incomingPackets: make(chan packetEntry, 10),
+		Incoming:        newQueue(),
+		Outgoing:        newQueue(),
 	}, nil
 }
 
@@ -196,7 +259,8 @@ func (p *QuicProxy) runProxy() error {
 				return err
 			}
 			p.clientDict[saddr] = conn
-			go p.runConnection(conn)
+			go p.runIncomingConnection(conn)
+			go p.runOutgoingConnection(conn)
 		}
 		p.mutex.Unlock()
 
@@ -207,75 +271,87 @@ func (p *QuicProxy) runProxy() error {
 			continue
 		}
 
-		// Send the packet to the server
 		delay := p.delayPacket(DirectionIncoming, raw)
-		if delay != 0 {
+		if delay == 0 {
 			if p.logger.Debug() {
-				p.logger.Debugf("delaying incoming packet (%d bytes) to %s by %s", n, conn.ServerConn.RemoteAddr(), delay)
-			}
-
-			p.mutex.Lock()
-			p.timerID++
-			id := p.timerID
-			timer := time.AfterFunc(delay, func() {
-				_, _ = conn.ServerConn.Write(raw) // TODO: handle error
-
-				p.mutex.Lock()
-				delete(p.timers, id)
-				p.mutex.Unlock()
-			})
-			p.timers[id] = timer
-			p.mutex.Unlock()
-		} else {
-			if p.logger.Debug() {
-				p.logger.Debugf("forwarding incoming packet (%d bytes) to %s", n, conn.ServerConn.RemoteAddr())
+				p.logger.Debugf("forwarding incoming packet (%d bytes) to %s", len(raw), conn.ServerConn.RemoteAddr())
 			}
 			if _, err := conn.ServerConn.Write(raw); err != nil {
 				return err
 			}
+		} else {
+			now := time.Now()
+			if p.logger.Debug() {
+				p.logger.Debugf("delaying incoming packet (%d bytes) to %s by %s", len(raw), conn.ServerConn.RemoteAddr(), delay)
+			}
+			conn.queuePacket(now.Add(delay), raw)
 		}
 	}
 }
 
 // runConnection handles packets from server to a single client
-func (p *QuicProxy) runConnection(conn *connection) error {
+func (p *QuicProxy) runOutgoingConnection(conn *connection) error {
+	outgoingPackets := make(chan packetEntry, 10)
+	go func() {
+		for {
+			buffer := make([]byte, protocol.MaxReceivePacketSize)
+			n, err := conn.ServerConn.Read(buffer)
+			if err != nil {
+				return
+			}
+			raw := buffer[0:n]
+
+			if p.dropPacket(DirectionOutgoing, raw) {
+				if p.logger.Debug() {
+					p.logger.Debugf("dropping outgoing packet(%d bytes)", n)
+				}
+				continue
+			}
+
+			delay := p.delayPacket(DirectionOutgoing, raw)
+			if delay == 0 {
+				if p.logger.Debug() {
+					p.logger.Debugf("forwarding outgoing packet (%d bytes) to %s", len(raw), conn.ClientAddr)
+				}
+				if _, err := p.conn.WriteToUDP(raw, conn.ClientAddr); err != nil {
+					return
+				}
+			} else {
+				now := time.Now()
+				if p.logger.Debug() {
+					p.logger.Debugf("delaying outgoing packet (%d bytes) to %s by %s", len(raw), conn.ClientAddr, delay)
+				}
+				outgoingPackets <- packetEntry{Time: now.Add(delay), Raw: raw}
+			}
+		}
+	}()
+
 	for {
-		buffer := make([]byte, protocol.MaxReceivePacketSize)
-		n, err := conn.ServerConn.Read(buffer)
-		if err != nil {
-			return err
-		}
-		raw := buffer[0:n]
-
-		if p.dropPacket(DirectionOutgoing, raw) {
-			if p.logger.Debug() {
-				p.logger.Debugf("dropping outgoing packet(%d bytes)", n)
-			}
-			continue
-		}
-
-		delay := p.delayPacket(DirectionOutgoing, raw)
-		if delay != 0 {
-			if p.logger.Debug() {
-				p.logger.Debugf("delaying outgoing packet (%d bytes) to %s by %s", n, conn.ClientAddr, delay)
-			}
-
-			p.mutex.Lock()
-			p.timerID++
-			id := p.timerID
-			timer := time.AfterFunc(delay, func() {
-				_, _ = p.conn.WriteToUDP(raw, conn.ClientAddr) // TODO: handle error
-				p.mutex.Lock()
-				delete(p.timers, id)
-				p.mutex.Unlock()
-			})
-			p.timers[id] = timer
-			p.mutex.Unlock()
-		} else {
-			if p.logger.Debug() {
-				p.logger.Debugf("forwarding outgoing packet (%d bytes) to %s", n, conn.ClientAddr)
-			}
-			if _, err := p.conn.WriteToUDP(raw, conn.ClientAddr); err != nil {
+		select {
+		case <-p.closeChan:
+			return nil
+		case e := <-outgoingPackets:
+			conn.Outgoing.Add(e)
+		case <-conn.Outgoing.Timer():
+			conn.Outgoing.SetTimerRead()
+			if _, err := p.conn.WriteTo(conn.Outgoing.Get(), conn.ClientAddr); err != nil {
+				return err
+			}
+		}
+	}
+}
+
+func (p *QuicProxy) runIncomingConnection(conn *connection) error {
+	for {
+		select {
+		case <-p.closeChan:
+			return nil
+		case e := <-conn.incomingPackets:
+			// Send the packet to the server
+			conn.Incoming.Add(e)
+		case <-conn.Incoming.Timer():
+			conn.Incoming.SetTimerRead()
+			if _, err := conn.ServerConn.Write(conn.Incoming.Get()); err != nil {
 				return err
 			}
 		}
diff --git a/integrationtests/tools/proxy/proxy_test.go b/integrationtests/tools/proxy/proxy_test.go
index 1b1403c6..ca6f2a08 100644
--- a/integrationtests/tools/proxy/proxy_test.go
+++ b/integrationtests/tools/proxy/proxy_test.go
@@ -19,11 +19,22 @@ import (
 
 type packetData []byte
 
+func isProxyRunning() bool {
+	var b bytes.Buffer
+	pprof.Lookup("goroutine").WriteTo(&b, 1)
+	return strings.Contains(b.String(), "proxy.(*QuicProxy).runIncomingConnection") ||
+		strings.Contains(b.String(), "proxy.(*QuicProxy).runOutgoingConnection")
+}
+
 var _ = Describe("QUIC Proxy", func() {
 	makePacket := func(p protocol.PacketNumber, payload []byte) []byte {
 		b := &bytes.Buffer{}
 		hdr := wire.ExtendedHeader{
 			Header: wire.Header{
+				IsLongHeader:     true,
+				Type:             protocol.PacketTypeInitial,
+				Version:          protocol.VersionTLS,
+				Length:           4 + protocol.ByteCount(len(payload)),
 				DestConnectionID: protocol.ConnectionID{0xde, 0xad, 0xbe, 0xef, 0, 0, 0x13, 0x37},
 				SrcConnectionID:  protocol.ConnectionID{0xde, 0xad, 0xbe, 0xef, 0, 0, 0x13, 0x37},
 			},
@@ -36,6 +47,19 @@ var _ = Describe("QUIC Proxy", func() {
 		return raw
 	}
 
+	readPacketNumber := func(b []byte) protocol.PacketNumber {
+		hdr, data, _, err := wire.ParsePacket(b, 0)
+		ExpectWithOffset(1, err).ToNot(HaveOccurred())
+		Expect(hdr.Type).To(Equal(protocol.PacketTypeInitial))
+		extHdr, err := hdr.ParseExtended(bytes.NewReader(data), protocol.VersionTLS)
+		ExpectWithOffset(1, err).ToNot(HaveOccurred())
+		return extHdr.PacketNumber
+	}
+
+	AfterEach(func() {
+		Eventually(isProxyRunning).Should(BeFalse())
+	})
+
 	Context("Proxy setup and teardown", func() {
 		It("sets up the UDPProxy", func() {
 			proxy, err := NewQuicProxy("localhost:0", nil)
@@ -80,12 +104,6 @@ var _ = Describe("QUIC Proxy", func() {
 		})
 
 		It("stops listening for proxied connections", func() {
-			isConnRunning := func() bool {
-				var b bytes.Buffer
-				pprof.Lookup("goroutine").WriteTo(&b, 1)
-				return strings.Contains(b.String(), "proxy.(*QuicProxy).runConnection")
-			}
-
 			serverAddr, err := net.ResolveUDPAddr("udp", "localhost:0")
 			Expect(err).ToNot(HaveOccurred())
 			serverConn, err := net.ListenUDP("udp", serverAddr)
@@ -94,16 +112,16 @@ var _ = Describe("QUIC Proxy", func() {
 
 			proxy, err := NewQuicProxy("localhost:0", &Opts{RemoteAddr: serverConn.LocalAddr().String()})
 			Expect(err).ToNot(HaveOccurred())
-			Expect(isConnRunning()).To(BeFalse())
+			Expect(isProxyRunning()).To(BeFalse())
 
 			// check that the proxy port is not in use anymore
 			conn, err := net.DialUDP("udp", nil, proxy.LocalAddr().(*net.UDPAddr))
 			Expect(err).ToNot(HaveOccurred())
 			_, err = conn.Write(makePacket(1, []byte("foobar")))
 			Expect(err).ToNot(HaveOccurred())
-			Eventually(isConnRunning).Should(BeTrue())
+			Eventually(isProxyRunning).Should(BeTrue())
 			Expect(proxy.Close()).To(Succeed())
-			Eventually(isConnRunning).Should(BeFalse())
+			Eventually(isProxyRunning).Should(BeFalse())
 		})
 
 		It("has the correct LocalAddr and LocalPort", func() {
@@ -284,16 +302,16 @@ var _ = Describe("QUIC Proxy", func() {
 		})
 
 		Context("Delay Callback", func() {
-			expectDelay := func(startTime time.Time, rtt time.Duration, numRTTs int) {
-				expectedReceiveTime := startTime.Add(time.Duration(numRTTs) * rtt)
+			const delay = 200 * time.Millisecond
+			expectDelay := func(startTime time.Time, numRTTs int) {
+				expectedReceiveTime := startTime.Add(time.Duration(numRTTs) * delay)
 				Expect(time.Now()).To(SatisfyAll(
 					BeTemporally(">=", expectedReceiveTime),
-					BeTemporally("<", expectedReceiveTime.Add(rtt/2)),
+					BeTemporally("<", expectedReceiveTime.Add(delay/2)),
 				))
 			}
 
 			It("delays incoming packets", func() {
-				delay := 300 * time.Millisecond
 				var counter int32
 				opts := &Opts{
 					RemoteAddr: serverConn.LocalAddr().String(),
@@ -317,16 +335,75 @@ var _ = Describe("QUIC Proxy", func() {
 					Expect(err).ToNot(HaveOccurred())
 				}
 				Eventually(serverReceivedPackets).Should(HaveLen(1))
-				expectDelay(start, delay, 1)
+				expectDelay(start, 1)
 				Eventually(serverReceivedPackets).Should(HaveLen(2))
-				expectDelay(start, delay, 2)
+				expectDelay(start, 2)
 				Eventually(serverReceivedPackets).Should(HaveLen(3))
-				expectDelay(start, delay, 3)
+				expectDelay(start, 3)
+				Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(1)))
+				Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(2)))
+				Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(3)))
+			})
+
+			It("handles reordered packets", func() {
+				var counter int32
+				opts := &Opts{
+					RemoteAddr: serverConn.LocalAddr().String(),
+					// delay packet 1 by 600 ms
+					// delay packet 2 by 400 ms
+					// delay packet 3 by 200 ms
+					DelayPacket: func(d Direction, _ []byte) time.Duration {
+						if d == DirectionOutgoing {
+							return 0
+						}
+						p := atomic.AddInt32(&counter, 1)
+						return 600*time.Millisecond - time.Duration(p-1)*delay
+					},
+				}
+				startProxy(opts)
+
+				// send 3 packets
+				start := time.Now()
+				for i := 1; i <= 3; i++ {
+					_, err := clientConn.Write(makePacket(protocol.PacketNumber(i), []byte("foobar"+strconv.Itoa(i))))
+					Expect(err).ToNot(HaveOccurred())
+				}
+				Eventually(serverReceivedPackets).Should(HaveLen(1))
+				expectDelay(start, 1)
+				Eventually(serverReceivedPackets).Should(HaveLen(2))
+				expectDelay(start, 2)
+				Eventually(serverReceivedPackets).Should(HaveLen(3))
+				expectDelay(start, 3)
+				Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(3)))
+				Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(2)))
+				Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(1)))
+			})
+
+			It("doesn't reorder packets when a constant delay is used", func() {
+				opts := &Opts{
+					RemoteAddr: serverConn.LocalAddr().String(),
+					DelayPacket: func(d Direction, _ []byte) time.Duration {
+						if d == DirectionOutgoing {
+							return 0
+						}
+						return 100 * time.Millisecond
+					},
+				}
+				startProxy(opts)
+
+				// send 100 packets
+				for i := 0; i < 100; i++ {
+					_, err := clientConn.Write(makePacket(protocol.PacketNumber(i), []byte("foobar"+strconv.Itoa(i))))
+					Expect(err).ToNot(HaveOccurred())
+				}
+				Eventually(serverReceivedPackets).Should(HaveLen(100))
+				for i := 0; i < 100; i++ {
+					Expect(readPacketNumber(<-serverReceivedPackets)).To(Equal(protocol.PacketNumber(i)))
+				}
 			})
 
 			It("delays outgoing packets", func() {
 				const numPackets = 3
-				delay := 300 * time.Millisecond
 				var counter int32
 				opts := &Opts{
 					RemoteAddr: serverConn.LocalAddr().String(),
@@ -365,13 +442,16 @@ var _ = Describe("QUIC Proxy", func() {
 				}
 				// the packets should have arrived immediately at the server
 				Eventually(serverReceivedPackets).Should(HaveLen(3))
-				expectDelay(start, delay, 0)
+				expectDelay(start, 0)
 				Eventually(clientReceivedPackets).Should(HaveLen(1))
-				expectDelay(start, delay, 1)
+				expectDelay(start, 1)
 				Eventually(clientReceivedPackets).Should(HaveLen(2))
-				expectDelay(start, delay, 2)
+				expectDelay(start, 2)
 				Eventually(clientReceivedPackets).Should(HaveLen(3))
-				expectDelay(start, delay, 3)
+				expectDelay(start, 3)
+				Expect(readPacketNumber(<-clientReceivedPackets)).To(Equal(protocol.PacketNumber(1)))
+				Expect(readPacketNumber(<-clientReceivedPackets)).To(Equal(protocol.PacketNumber(2)))
+				Expect(readPacketNumber(<-clientReceivedPackets)).To(Equal(protocol.PacketNumber(3)))
 			})
 		})
 	})