diff --git a/middleware.go b/middleware.go
index 9ad9c48..ac73c7d 100644
--- a/middleware.go
+++ b/middleware.go
@@ -1,9 +1,11 @@
 package nethttp
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"log"
+	"net"
 	"net/http"
 	"strconv"
 
@@ -87,6 +89,11 @@ func (m *middleware) wrap(next http.Handler) http.Handler {
 		observed := &statusObserver{ResponseWriter: w, capture: capture,
 			hold: m.engine.Config.CustomResponseModifier != nil}
 		next.ServeHTTP(observed, r)
+		if observed.hijacked {
+			// The handler took over the connection (websocket upgrade, raw
+			// stream): nothing is left to observe, modify or write.
+			return
+		}
 		m.engine.ProcessResponse(req, &guardcore.Response{
 			StatusCode: observed.status(),
 			Headers:    map[string]string{},
@@ -109,6 +116,44 @@ type statusObserver struct {
 	statusCode  int
 	hold        bool
 	held        []byte
+	hijacked    bool
+}
+
+// Unwrap exposes the underlying writer so http.ResponseController reaches
+// the optional interfaces (deadlines, full duplex, ...) the observer does
+// not wrap itself.
+func (o *statusObserver) Unwrap() http.ResponseWriter { return o.ResponseWriter }
+
+// Flush implements http.Flusher. In pass-through mode it pins the implicit
+// 200 the real writer is about to send and delegates. In hold mode the
+// response is buffered for the CustomResponseModifier (which must see all
+// of it), so Flush is a no-op there and the response is sent at release.
+func (o *statusObserver) Flush() {
+	if o.hold || o.hijacked {
+		return
+	}
+	if !o.wroteHeader {
+		o.statusCode = http.StatusOK
+		o.wroteHeader = true
+	}
+	if f, ok := o.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
+// Hijack implements http.Hijacker by delegating to the underlying writer.
+// A hijacked connection is left alone: the middleware neither releases a
+// held response nor runs the response pass over it.
+func (o *statusObserver) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	h, ok := o.ResponseWriter.(http.Hijacker)
+	if !ok {
+		return nil, nil, http.ErrNotSupported
+	}
+	conn, rw, err := h.Hijack()
+	if err == nil {
+		o.hijacked = true
+	}
+	return conn, rw, err
 }
 
 func (o *statusObserver) WriteHeader(code int) {
diff --git a/observer_test.go b/observer_test.go
new file mode 100644
index 0000000..283c21c
--- /dev/null
+++ b/observer_test.go
@@ -0,0 +1,187 @@
+package nethttp
+
+import (
+	"bufio"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/rennf93/guard-core-go/v4/guardcore"
+)
+
+func modifierConfig(c *guardcore.SecurityConfig) {
+	c.CustomResponseModifier = func(resp *guardcore.Response) *guardcore.Response {
+		resp.SetHeader("X-Modified", "yes")
+		return resp
+	}
+}
+
+func startGuarded(t *testing.T, mutate func(*guardcore.SecurityConfig), h http.HandlerFunc) *httptest.Server {
+	t.Helper()
+	wrap, _ := newTestMiddleware(t, mutate)
+	srv := httptest.NewServer(wrap(h))
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+func TestObserverFlushStreamsThroughRealServer(t *testing.T) {
+	release := make(chan struct{})
+	srv := startGuarded(t, nil, func(w http.ResponseWriter, r *http.Request) {
+		f, ok := w.(http.Flusher)
+		if !ok {
+			t.Error("the wrapped writer must expose http.Flusher")
+			return
+		}
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte("data: one\n\n"))
+		f.Flush()
+		<-release
+		_, _ = w.Write([]byte("data: two\n\n"))
+	})
+	resp, err := http.Get(srv.URL + "/stream")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	line, err := bufio.NewReader(resp.Body).ReadString('\n')
+	if err != nil || line != "data: one\n" {
+		t.Fatalf("first event must arrive before the handler finishes, got %q err %v", line, err)
+	}
+	close(release)
+}
+
+func TestObserverResponseControllerFlushAndUnwrap(t *testing.T) {
+	release := make(chan struct{})
+	srv := startGuarded(t, nil, func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte("first\n"))
+		if err := http.NewResponseController(w).Flush(); err != nil {
+			t.Errorf("ResponseController.Flush: %v", err)
+		}
+		<-release
+	})
+	resp, err := http.Get(srv.URL + "/rc")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	line, _ := bufio.NewReader(resp.Body).ReadString('\n')
+	if line != "first\n" {
+		t.Fatalf("got %q", line)
+	}
+	close(release)
+}
+
+func TestObserverUnwrapReturnsUnderlyingWriter(t *testing.T) {
+	rec := httptest.NewRecorder()
+	o := &statusObserver{ResponseWriter: rec}
+	if o.Unwrap() != http.ResponseWriter(rec) {
+		t.Fatal("Unwrap must return the underlying writer")
+	}
+}
+
+func TestObserverFlushRecordsImplicitStatus(t *testing.T) {
+	rec := httptest.NewRecorder()
+	o := &statusObserver{ResponseWriter: rec}
+	o.Flush()
+	if !rec.Flushed || o.status() != http.StatusOK || !o.wroteHeader {
+		t.Fatalf("flush must delegate and pin the implicit 200 (flushed=%v status=%d)", rec.Flushed, o.status())
+	}
+}
+
+func TestObserverHijackUnsupportedWriter(t *testing.T) {
+	o := &statusObserver{ResponseWriter: httptest.NewRecorder()}
+	if _, _, err := o.Hijack(); err != http.ErrNotSupported {
+		t.Fatalf("a non-hijackable writer must answer http.ErrNotSupported, got %v", err)
+	}
+}
+
+func hijackUpgrade(t *testing.T, srv *httptest.Server) string {
+	t.Helper()
+	conn, err := net.Dial("tcp", strings.TrimPrefix(srv.URL, "http://"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+	_ = conn.SetDeadline(time.Now().Add(5 * time.Second))
+	_, _ = conn.Write([]byte("GET /ws HTTP/1.1\r\nHost: x\r\nConnection: Upgrade\r\nUpgrade: raw\r\n\r\n"))
+	rd := bufio.NewReader(conn)
+	status, err := rd.ReadString('\n')
+	if err != nil || !strings.HasPrefix(status, "HTTP/1.1 101") {
+		t.Fatalf("expected the hijacked 101 handshake, got %q err %v", status, err)
+	}
+	for {
+		line, err := rd.ReadString('\n')
+		if err != nil {
+			t.Fatal(err)
+		}
+		if line == "\r\n" {
+			break
+		}
+	}
+	payload, err := rd.ReadString('\n')
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _ = conn.Write([]byte("ping\n"))
+	echo, err := rd.ReadString('\n')
+	if err != nil {
+		t.Fatal(err)
+	}
+	return payload + echo
+}
+
+func hijackHandler(t *testing.T) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		h, ok := w.(http.Hijacker)
+		if !ok {
+			t.Error("the wrapped writer must expose http.Hijacker")
+			return
+		}
+		conn, rw, err := h.Hijack()
+		if err != nil {
+			t.Errorf("hijack: %v", err)
+			return
+		}
+		defer conn.Close()
+		_, _ = rw.WriteString("HTTP/1.1 101 Switching Protocols\r\nConnection: Upgrade\r\nUpgrade: raw\r\n\r\nhello\n")
+		_ = rw.Flush()
+		line, _ := rw.ReadString('\n')
+		_, _ = rw.WriteString("echo:" + line)
+		_ = rw.Flush()
+	}
+}
+
+func TestObserverHijackThroughRealServer(t *testing.T) {
+	srv := startGuarded(t, nil, hijackHandler(t))
+	if got := hijackUpgrade(t, srv); got != "hello\necho:ping\n" {
+		t.Fatalf("raw hijack exchange: %q", got)
+	}
+}
+
+func TestObserverHijackLeftAloneWithResponseModifier(t *testing.T) {
+	srv := startGuarded(t, modifierConfig, hijackHandler(t))
+	if got := hijackUpgrade(t, srv); got != "hello\necho:ping\n" {
+		t.Fatalf("hijack with a CustomResponseModifier must not be released over: %q", got)
+	}
+}
+
+func TestObserverHeldWriterStillAppliesModifierAfterFlush(t *testing.T) {
+	srv := startGuarded(t, modifierConfig, func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte("part1,"))
+		w.(http.Flusher).Flush()
+		_, _ = w.Write([]byte("part2"))
+	})
+	resp, err := http.Get(srv.URL + "/held")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	buf := make([]byte, 64)
+	n, _ := resp.Body.Read(buf)
+	if resp.Header.Get("X-Modified") != "yes" || string(buf[:n]) != "part1,part2" {
+		t.Fatalf("held response must be modified and complete, got %q header %q", buf[:n], resp.Header.Get("X-Modified"))
+	}
+}