diff --git a/client.go b/client.go
index 3c6aefb3..5fbeb856 100644
--- a/client.go
+++ b/client.go
@@ -331,7 +331,6 @@ func (c *client) handlePacket(remoteAddr net.Addr, packet []byte) error {
 }
 
 func (c *client) handleIETFQUICPacket(hdr *wire.Header, packetData []byte, remoteAddr net.Addr, rcvTime time.Time) error {
-	// TODO(#1003): add support for server-chosen connection IDs
 	// reject packets with the wrong connection ID
 	if !hdr.DestConnectionID.Equal(c.srcConnID) {
 		return fmt.Errorf("received a packet with an unexpected connection ID (%s, expected %s)", hdr.DestConnectionID, c.srcConnID)
diff --git a/server.go b/server.go
index 963801b7..ea0ab833 100644
--- a/server.go
+++ b/server.go
@@ -165,15 +165,10 @@ func (s *server) setupTLS() error {
 			case <-s.errorChan:
 				return
 			case tlsSession := <-sessionChan:
-				connID := tlsSession.connID
 				sess := tlsSession.sess
-				if _, ok := s.sessionHandler.Get(connID); ok { // drop this session if it already exists
-					continue
-				}
-				// TODO(#1003): There's a race condition here.
-				// If another connection with the same conn ID is added between Get() and Add(), it would be overwritten.
-				// We can avoid this be using server-chosen connection IDs.
-				s.sessionHandler.Add(connID, sess)
+				// The connection ID is a randomly chosen 8 byte value.
+				// It is safe to assume that it doesn't collide with other randomly chosen values.
+				s.sessionHandler.Add(tlsSession.connID, sess)
 				go sess.run()
 			}
 		}
diff --git a/server_test.go b/server_test.go
index 8e2df4e4..9f214e6b 100644
--- a/server_test.go
+++ b/server_test.go
@@ -158,7 +158,6 @@ var _ = Describe("Server", func() {
 			sess.EXPECT().run().Do(func() { close(run) })
 			err := serv.setupTLS()
 			Expect(err).ToNot(HaveOccurred())
-			sessionHandler.EXPECT().Get(connID)
 			sessionHandler.EXPECT().Add(connID, sess)
 			serv.serverTLS.sessionChan <- tlsSession{
 				connID: connID,
@@ -167,24 +166,6 @@ var _ = Describe("Server", func() {
 			Eventually(run).Should(BeClosed())
 		})
 
-		It("only accepts one new TLS sessions for one connection ID", func() {
-			connID := protocol.ConnectionID{1, 2, 3, 4, 5, 6, 7, 8}
-			sess := NewMockPacketHandler(mockCtrl)
-			err := serv.setupTLS()
-			Expect(err).ToNot(HaveOccurred())
-
-			done := make(chan struct{})
-			sessionHandler.EXPECT().Get(connID).Return(NewMockPacketHandler(mockCtrl), true).Do(func(protocol.ConnectionID) {
-				close(done)
-			})
-			// don't EXPECT any calls to sessionHandler.Add
-			serv.serverTLS.sessionChan <- tlsSession{
-				connID: connID,
-				sess:   sess,
-			}
-			Eventually(done).Should(BeClosed())
-		})
-
 		It("accepts a session once the connection it is forward secure", func() {
 			s := NewMockPacketHandler(mockCtrl)
 			s.EXPECT().handlePacket(gomock.Any())
diff --git a/server_tls.go b/server_tls.go
index 5d1f4ea1..fecdf523 100644
--- a/server_tls.go
+++ b/server_tls.go
@@ -92,7 +92,7 @@ func newServerTLS(
 func (s *serverTLS) HandleInitial(remoteAddr net.Addr, hdr *wire.Header, data []byte) {
 	// TODO: add a check that DestConnID == SrcConnID
 	s.logger.Debugf("Received a Packet. Handling it statelessly.")
-	sess, err := s.handleInitialImpl(remoteAddr, hdr, data)
+	sess, connID, err := s.handleInitialImpl(remoteAddr, hdr, data)
 	if err != nil {
 		s.logger.Errorf("Error occurred handling initial packet: %s", err)
 		return
@@ -101,7 +101,7 @@ func (s *serverTLS) HandleInitial(remoteAddr net.Addr, hdr *wire.Header, data []
 		return
 	}
 	s.sessionChan <- tlsSession{
-		connID: hdr.DestConnectionID,
+		connID: connID,
 		sess:   sess,
 	}
 }
@@ -135,48 +135,48 @@ func (s *serverTLS) sendConnectionClose(remoteAddr net.Addr, clientHdr *wire.Hea
 	return err
 }
 
-func (s *serverTLS) handleInitialImpl(remoteAddr net.Addr, hdr *wire.Header, data []byte) (packetHandler, error) {
+func (s *serverTLS) handleInitialImpl(remoteAddr net.Addr, hdr *wire.Header, data []byte) (packetHandler, protocol.ConnectionID, error) {
 	if len(hdr.Raw)+len(data) < protocol.MinInitialPacketSize {
-		return nil, errors.New("dropping too small Initial packet")
+		return nil, nil, errors.New("dropping too small Initial packet")
 	}
 	// check version, if not matching send VNP
 	if !protocol.IsSupportedVersion(s.supportedVersions, hdr.Version) {
 		s.logger.Debugf("Client offered version %s, sending VersionNegotiationPacket", hdr.Version)
 		vnp, err := wire.ComposeVersionNegotiation(hdr.SrcConnectionID, hdr.DestConnectionID, s.supportedVersions)
 		if err != nil {
-			return nil, err
+			return nil, nil, err
 		}
 		_, err = s.conn.WriteTo(vnp, remoteAddr)
-		return nil, err
+		return nil, nil, err
 	}
 
 	// unpack packet and check stream frame contents
 	aead, err := crypto.NewNullAEAD(protocol.PerspectiveServer, hdr.DestConnectionID, protocol.VersionTLS)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	frame, err := unpackInitialPacket(aead, hdr, data, s.logger, hdr.Version)
 	if err != nil {
 		s.logger.Debugf("Error unpacking initial packet: %s", err)
-		return nil, nil
+		return nil, nil, nil
 	}
-	sess, err := s.handleUnpackedInitial(remoteAddr, hdr, frame, aead)
+	sess, connID, err := s.handleUnpackedInitial(remoteAddr, hdr, frame, aead)
 	if err != nil {
 		if ccerr := s.sendConnectionClose(remoteAddr, hdr, aead, err); ccerr != nil {
 			s.logger.Debugf("Error sending CONNECTION_CLOSE: %s", ccerr)
 		}
-		return nil, err
+		return nil, nil, err
 	}
-	return sess, nil
+	return sess, connID, nil
 }
 
-func (s *serverTLS) handleUnpackedInitial(remoteAddr net.Addr, hdr *wire.Header, frame *wire.StreamFrame, aead crypto.AEAD) (packetHandler, error) {
+func (s *serverTLS) handleUnpackedInitial(remoteAddr net.Addr, hdr *wire.Header, frame *wire.StreamFrame, aead crypto.AEAD) (packetHandler, protocol.ConnectionID, error) {
 	version := hdr.Version
 	bc := handshake.NewCryptoStreamConn(remoteAddr)
 	bc.AddDataForReading(frame.Data)
 	tls, paramsChan, err := s.newMintConn(bc, version)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	alert := tls.Handshake()
 	if alert == mint.AlertStatelessRetry {
@@ -197,29 +197,34 @@ func (s *serverTLS) handleUnpackedInitial(remoteAddr net.Addr, hdr *wire.Header,
 		}
 		data, err := packUnencryptedPacket(aead, replyHdr, f, protocol.PerspectiveServer, s.logger)
 		if err != nil {
-			return nil, err
+			return nil, nil, err
 		}
 		_, err = s.conn.WriteTo(data, remoteAddr)
-		return nil, err
+		return nil, nil, err
 	}
 	if alert != mint.AlertNoAlert {
-		return nil, alert
+		return nil, nil, alert
 	}
 	if tls.State() != mint.StateServerNegotiated {
-		return nil, fmt.Errorf("Expected mint state to be %s, got %s", mint.StateServerNegotiated, tls.State())
+		return nil, nil, fmt.Errorf("Expected mint state to be %s, got %s", mint.StateServerNegotiated, tls.State())
 	}
 	if alert := tls.Handshake(); alert != mint.AlertNoAlert {
-		return nil, alert
+		return nil, nil, alert
 	}
 	if tls.State() != mint.StateServerWaitFlight2 {
-		return nil, fmt.Errorf("Expected mint state to be %s, got %s", mint.StateServerWaitFlight2, tls.State())
+		return nil, nil, fmt.Errorf("Expected mint state to be %s, got %s", mint.StateServerWaitFlight2, tls.State())
 	}
 	params := <-paramsChan
+	connID, err := protocol.GenerateConnectionID()
+	if err != nil {
+		return nil, nil, err
+	}
+	s.logger.Debugf("Changing source connection ID to %s.", connID)
 	sess, err := newTLSServerSession(
 		&conn{pconn: s.conn, currentAddr: remoteAddr},
 		s.sessionRunner,
 		hdr.SrcConnectionID,
-		hdr.DestConnectionID,     // TODO(#1003): we can use a server-chosen connection ID here
+		connID,
 		protocol.PacketNumber(1), // TODO: use a random packet number here
 		s.config,
 		tls,
@@ -230,10 +235,10 @@ func (s *serverTLS) handleUnpackedInitial(remoteAddr net.Addr, hdr *wire.Header,
 		s.logger,
 	)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	cs := sess.getCryptoStream()
 	cs.setReadOffset(frame.DataLen())
 	bc.SetStream(cs)
-	return sess, nil
+	return sess, connID, nil
 }
diff --git a/server_tls_test.go b/server_tls_test.go
index 4d4e764d..03122aca 100644
--- a/server_tls_test.go
+++ b/server_tls_test.go
@@ -146,7 +146,11 @@ var _ = Describe("Stateless TLS handling", func() {
 			Expect(conn.dataWritten.Len()).To(BeZero())
 			close(done)
 		}()
-		Eventually(sessionChan).Should(Receive())
+		var tlsSess tlsSession
+		Eventually(sessionChan).Should(Receive(&tlsSess))
+		// make sure we're using a server-generated connection ID
+		Expect(tlsSess.connID).ToNot(Equal(hdr.SrcConnectionID))
+		Expect(tlsSess.connID).ToNot(Equal(hdr.DestConnectionID))
 		Eventually(done).Should(BeClosed())
 	})