diff --git a/internal/utils/atomic_bool.go b/internal/utils/atomic_bool.go
new file mode 100644
index 00000000000..cf4642504e0
--- /dev/null
+++ b/internal/utils/atomic_bool.go
@@ -0,0 +1,22 @@
+package utils
+
+import "sync/atomic"
+
+// An AtomicBool is an atomic bool
+type AtomicBool struct {
+	v int32
+}
+
+// Set sets the value
+func (a *AtomicBool) Set(value bool) {
+	var n int32
+	if value {
+		n = 1
+	}
+	atomic.StoreInt32(&a.v, n)
+}
+
+// Get gets the value
+func (a *AtomicBool) Get() bool {
+	return atomic.LoadInt32(&a.v) != 0
+}
diff --git a/internal/utils/atomic_bool_test.go b/internal/utils/atomic_bool_test.go
new file mode 100644
index 00000000000..83a200c2781
--- /dev/null
+++ b/internal/utils/atomic_bool_test.go
@@ -0,0 +1,29 @@
+package utils
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Atomic Bool", func() {
+	var a *AtomicBool
+
+	BeforeEach(func() {
+		a = &AtomicBool{}
+	})
+
+	It("has the right default value", func() {
+		Expect(a.Get()).To(BeFalse())
+	})
+
+	It("sets the value to true", func() {
+		a.Set(true)
+		Expect(a.Get()).To(BeTrue())
+	})
+
+	It("sets the value to false", func() {
+		a.Set(true)
+		a.Set(false)
+		Expect(a.Get()).To(BeFalse())
+	})
+})
diff --git a/packet_handler_map.go b/packet_handler_map.go
index fef9468ed9d..4f3b69507f3 100644
--- a/packet_handler_map.go
+++ b/packet_handler_map.go
@@ -56,10 +56,6 @@ func (h *packetHandlerMap) Remove(id protocol.ConnectionID) {
 }
 
 func (h *packetHandlerMap) removeByConnectionIDAsString(id string) {
-	h.mutex.Lock()
-	h.handlers[id] = nil
-	h.mutex.Unlock()
-
 	time.AfterFunc(h.deleteClosedSessionsAfter, func() {
 		h.mutex.Lock()
 		delete(h.handlers, id)
@@ -102,13 +98,11 @@ func (h *packetHandlerMap) close(e error) error {
 
 	var wg sync.WaitGroup
 	for _, handler := range h.handlers {
-		if handler != nil {
-			wg.Add(1)
-			go func(handler packetHandler) {
-				handler.destroy(e)
-				wg.Done()
-			}(handler)
-		}
+		wg.Add(1)
+		go func(handler packetHandler) {
+			handler.destroy(e)
+			wg.Done()
+		}(handler)
 	}
 
 	if h.server != nil {
diff --git a/packet_handler_map_test.go b/packet_handler_map_test.go
index c5f1b267a3c..bc18c561ec2 100644
--- a/packet_handler_map_test.go
+++ b/packet_handler_map_test.go
@@ -88,20 +88,23 @@ var _ = Describe("Packet Handler Map", func() {
 			Expect(err.Error()).To(ContainSubstring("error parsing invariant header:"))
 		})
 
-		It("deletes nil session entries after a wait time", func() {
+		It("deletes closed session entries after a wait time", func() {
 			handler.deleteClosedSessionsAfter = 10 * time.Millisecond
 			connID := protocol.ConnectionID{1, 2, 3, 4, 5, 6, 7, 8}
 			handler.Add(connID, NewMockPacketHandler(mockCtrl))
 			handler.Remove(connID)
-			Eventually(func() error {
-				return handler.handlePacket(nil, getPacket(connID))
-			}).Should(MatchError("received a packet with an unexpected connection ID 0x0102030405060708"))
+			time.Sleep(30 * time.Millisecond)
+			Expect(handler.handlePacket(nil, getPacket(connID))).To(MatchError("received a packet with an unexpected connection ID 0x0102030405060708"))
 		})
 
-		It("ignores packets arriving late for closed sessions", func() {
+		It("passes packets arriving late for closed sessions to that session", func() {
 			handler.deleteClosedSessionsAfter = time.Hour
 			connID := protocol.ConnectionID{1, 2, 3, 4, 5, 6, 7, 8}
-			handler.Add(connID, NewMockPacketHandler(mockCtrl))
+			packetHandler := NewMockPacketHandler(mockCtrl)
+			packetHandler.EXPECT().GetVersion().Return(protocol.VersionWhatever)
+			packetHandler.EXPECT().GetPerspective().Return(protocol.PerspectiveClient)
+			packetHandler.EXPECT().handlePacket(gomock.Any())
+			handler.Add(connID, packetHandler)
 			handler.Remove(connID)
 			err := handler.handlePacket(nil, getPacket(connID))
 			Expect(err).ToNot(HaveOccurred())
diff --git a/session.go b/session.go
index a55daf8bec9..2304455c1dc 100644
--- a/session.go
+++ b/session.go
@@ -94,9 +94,13 @@ type session struct {
 
 	receivedPackets  chan *receivedPacket
 	sendingScheduled chan struct{}
-	// closeChan is used to notify the run loop that it should terminate.
-	closeChan chan closeError
+
 	closeOnce sync.Once
+	closed    utils.AtomicBool
+	// closeChan is used to notify the run loop that it should terminate
+	closeChan                 chan closeError
+	connectionClosePacket     *packedPacket
+	packetsReceivedAfterClose int
 
 	ctx       context.Context
 	ctxCancel context.CancelFunc
@@ -418,6 +422,7 @@ runLoop:
 	if err := s.handleCloseError(closeErr); err != nil {
 		s.logger.Infof("Handling close error failed: %s", err)
 	}
+	s.closed.Set(true)
 	s.logger.Infof("Connection %s closed.", s.srcConnID)
 	s.sessionRunner.removeConnectionID(s.srcConnID)
 	s.cryptoStreamHandler.Close()
@@ -596,6 +601,9 @@ func (s *session) handleFrames(fs []wire.Frame, encLevel protocol.EncryptionLeve
 
 // handlePacket is called by the server with a new packet
 func (s *session) handlePacket(p *receivedPacket) {
+	if s.closed.Get() {
+		s.handlePacketAfterClosed(p)
+	}
 	// Discard packets once the amount of queued packets is larger than
 	// the channel size, protocol.MaxSessionUnprocessedPackets
 	select {
@@ -604,6 +612,24 @@ func (s *session) handlePacket(p *receivedPacket) {
 	}
 }
 
+func (s *session) handlePacketAfterClosed(p *receivedPacket) {
+	s.packetsReceivedAfterClose++
+	if s.connectionClosePacket == nil {
+		return
+	}
+	// exponential backoff
+	// only send a CONNECTION_CLOSE for the 1st, 2nd, 4th, 8th, 16th, ... packet arriving
+	for n := s.packetsReceivedAfterClose; n > 1; n = n / 2 {
+		if n%2 != 0 {
+			return
+		}
+	}
+	s.logger.Debugf("Received %d packets after sending CONNECTION_CLOSE. Retransmitting.", s.packetsReceivedAfterClose)
+	if err := s.conn.Write(s.connectionClosePacket.raw); err != nil {
+		s.logger.Debugf("Error retransmitting CONNECTION_CLOSE: %s", err)
+	}
+}
+
 func (s *session) handleCryptoFrame(frame *wire.CryptoFrame, encLevel protocol.EncryptionLevel) error {
 	encLevelChanged, err := s.cryptoStreamManager.HandleCryptoFrame(frame, encLevel)
 	if err != nil {
@@ -943,6 +969,7 @@ func (s *session) sendConnectionClose(quicErr *qerr.QuicError) error {
 	if err != nil {
 		return err
 	}
+	s.connectionClosePacket = packet
 	s.logPacket(packet)
 	return s.conn.Write(packet.raw)
 }
diff --git a/session_test.go b/session_test.go
index 54b94c8df49..7ab2bf1b1f2 100644
--- a/session_test.go
+++ b/session_test.go
@@ -426,6 +426,24 @@ var _ = Describe("Session", func() {
 			sess.Close()
 			Eventually(returned).Should(BeClosed())
 		})
+
+		It("retransmits the CONNECTION_CLOSE packet if packets are arriving late", func() {
+			streamManager.EXPECT().CloseWithError(gomock.Any())
+			sessionRunner.EXPECT().removeConnectionID(gomock.Any())
+			cryptoSetup.EXPECT().Close()
+			packer.EXPECT().PackConnectionClose(gomock.Any()).Return(&packedPacket{raw: []byte("foobar")}, nil)
+			sess.Close()
+			Expect(mconn.written).To(Receive(Equal([]byte("foobar")))) // receive the CONNECTION_CLOSE
+			Eventually(sess.Context().Done()).Should(BeClosed())
+			for i := 1; i <= 20; i++ {
+				sess.handlePacket(&receivedPacket{})
+				if i == 1 || i == 2 || i == 4 || i == 8 || i == 16 {
+					Expect(mconn.written).To(Receive(Equal([]byte("foobar")))) // receive the CONNECTION_CLOSE
+				} else {
+					Expect(mconn.written).To(HaveLen(0))
+				}
+			}
+		})
 	})
 
 	Context("receiving packets", func() {