diff --git a/h2quic/response_writer.go b/h2quic/response_writer.go
index fc0d8a45..a730e34c 100644
--- a/h2quic/response_writer.go
+++ b/h2quic/response_writer.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"net/http"
 	"strconv"
+	"sync"
 
 	"github.com/lucas-clemente/quic-go/protocol"
 	"github.com/lucas-clemente/quic-go/utils"
@@ -13,19 +14,22 @@ import (
 
 type responseWriter struct {
 	dataStreamID protocol.StreamID
-	headerStream utils.Stream
 	dataStream   utils.Stream
 
+	headerStream      utils.Stream
+	headerStreamMutex *sync.Mutex
+
 	header        http.Header
 	headerWritten bool
 }
 
-func newResponseWriter(headerStream, dataStream utils.Stream, dataStreamID protocol.StreamID) *responseWriter {
+func newResponseWriter(headerStream utils.Stream, headerStreamMutex *sync.Mutex, dataStream utils.Stream, dataStreamID protocol.StreamID) *responseWriter {
 	return &responseWriter{
-		header:       http.Header{},
-		headerStream: headerStream,
-		dataStream:   dataStream,
-		dataStreamID: dataStreamID,
+		header:            http.Header{},
+		headerStream:      headerStream,
+		headerStreamMutex: headerStreamMutex,
+		dataStream:        dataStream,
+		dataStreamID:      dataStreamID,
 	}
 }
 
@@ -45,6 +49,8 @@ func (w *responseWriter) WriteHeader(status int) {
 	}
 
 	utils.Infof("Responding with %d", status)
+	w.headerStreamMutex.Lock()
+	defer w.headerStreamMutex.Unlock()
 	h2framer := http2.NewFramer(w.headerStream, nil)
 	err := h2framer.WriteHeaders(http2.HeadersFrameParam{
 		StreamID:      uint32(w.dataStreamID),
diff --git a/h2quic/response_writer_test.go b/h2quic/response_writer_test.go
index 0a042585..0448c015 100644
--- a/h2quic/response_writer_test.go
+++ b/h2quic/response_writer_test.go
@@ -3,6 +3,7 @@ package h2quic
 import (
 	"bytes"
 	"net/http"
+	"sync"
 
 	"github.com/lucas-clemente/quic-go/protocol"
 	. "github.com/onsi/ginkgo"
@@ -29,7 +30,7 @@ var _ = Describe("Response Writer", func() {
 	BeforeEach(func() {
 		headerStream = &mockStream{}
 		dataStream = &mockStream{}
-		w = newResponseWriter(headerStream, dataStream, 5)
+		w = newResponseWriter(headerStream, &sync.Mutex{}, dataStream, 5)
 	})
 
 	It("writes status", func() {
diff --git a/h2quic/server.go b/h2quic/server.go
index eeb99874..94dddf76 100644
--- a/h2quic/server.go
+++ b/h2quic/server.go
@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"net"
 	"net/http"
+	"sync"
 	"time"
 
 	"github.com/lucas-clemente/quic-go"
@@ -83,8 +84,9 @@ func (s *Server) handleStream(session streamCreator, stream utils.Stream) {
 	h2framer := http2.NewFramer(nil, stream)
 
 	go func() {
+		var headerStreamMutex sync.Mutex // Protects concurrent calls to Write()
 		for {
-			if err := s.handleRequest(session, stream, hpackDecoder, h2framer); err != nil {
+			if err := s.handleRequest(session, stream, &headerStreamMutex, hpackDecoder, h2framer); err != nil {
 				utils.Errorf("error handling h2 request: %s", err.Error())
 				return
 			}
@@ -92,7 +94,7 @@ func (s *Server) handleStream(session streamCreator, stream utils.Stream) {
 	}()
 }
 
-func (s *Server) handleRequest(session streamCreator, headerStream utils.Stream, hpackDecoder *hpack.Decoder, h2framer *http2.Framer) error {
+func (s *Server) handleRequest(session streamCreator, headerStream utils.Stream, headerStreamMutex *sync.Mutex, hpackDecoder *hpack.Decoder, h2framer *http2.Framer) error {
 	h2frame, err := h2framer.ReadFrame()
 	if err != nil {
 		return err
@@ -125,7 +127,7 @@ func (s *Server) handleRequest(session streamCreator, headerStream utils.Stream,
 	// stream's Close() closes the write side, not the read side
 	req.Body = ioutil.NopCloser(dataStream)
 
-	responseWriter := newResponseWriter(headerStream, dataStream, protocol.StreamID(h2headersFrame.StreamID))
+	responseWriter := newResponseWriter(headerStream, headerStreamMutex, dataStream, protocol.StreamID(h2headersFrame.StreamID))
 
 	go func() {
 		handler := s.Handler
diff --git a/h2quic/server_test.go b/h2quic/server_test.go
index 9fcd13bc..bc54c1bd 100644
--- a/h2quic/server_test.go
+++ b/h2quic/server_test.go
@@ -2,6 +2,7 @@ package h2quic
 
 import (
 	"net/http"
+	"sync"
 
 	"golang.org/x/net/http2"
 	"golang.org/x/net/http2/hpack"
@@ -66,7 +67,7 @@ var _ = Describe("H2 server", func() {
 				// Taken from https://http2.github.io/http2-spec/compression.html#request.examples.with.huffman.coding
 				0x82, 0x86, 0x84, 0x41, 0x8c, 0xf1, 0xe3, 0xc2, 0xe5, 0xf2, 0x3a, 0x6b, 0xa0, 0xab, 0x90, 0xf4, 0xff,
 			})
-			err := s.handleRequest(session, headerStream, hpackDecoder, h2framer)
+			err := s.handleRequest(session, headerStream, &sync.Mutex{}, hpackDecoder, h2framer)
 			Expect(err).NotTo(HaveOccurred())
 			Eventually(func() bool { return handlerCalled }).Should(BeTrue())
 			Expect(dataStream.remoteClosed).To(BeTrue())
@@ -83,7 +84,7 @@ var _ = Describe("H2 server", func() {
 				// Taken from https://http2.github.io/http2-spec/compression.html#request.examples.with.huffman.coding
 				0x82, 0x86, 0x84, 0x41, 0x8c, 0xf1, 0xe3, 0xc2, 0xe5, 0xf2, 0x3a, 0x6b, 0xa0, 0xab, 0x90, 0xf4, 0xff,
 			})
-			err := s.handleRequest(session, headerStream, hpackDecoder, h2framer)
+			err := s.handleRequest(session, headerStream, &sync.Mutex{}, hpackDecoder, h2framer)
 			Expect(err).NotTo(HaveOccurred())
 			Eventually(func() bool { return handlerCalled }).Should(BeTrue())
 			Expect(dataStream.remoteClosed).To(BeFalse())
diff --git a/stream.go b/stream.go
index fb46d82a..29e008e4 100644
--- a/stream.go
+++ b/stream.go
@@ -25,6 +25,8 @@ var (
 )
 
 // A Stream assembles the data from StreamFrames and provides a super-convenient Read-Interface
+//
+// Read() and Write() may be called concurrently, but multiple calls to Read() or Write() individually must be synchronized manually.
 type stream struct {
 	streamID protocol.StreamID
 	session  streamHandler