diff --git a/hijack.go b/hijack.go
index 477dd992..a02d4f33 100644
--- a/hijack.go
+++ b/hijack.go
@@ -356,6 +356,31 @@ func (ctx *HijackResponse) Headers() http.Header {
 
 // SetHeader of the payload via key-value pairs.
 func (ctx *HijackResponse) SetHeader(pairs ...string) *HijackResponse {
+	headerIndex := make(map[string]int, len(ctx.payload.ResponseHeaders))
+	for i, header := range ctx.payload.ResponseHeaders {
+		headerIndex[header.Name] = i
+	}
+
+	for i := 0; i < len(pairs); i += 2 {
+		name := pairs[i]
+		value := pairs[i+1]
+
+		if idx, exists := headerIndex[name]; exists {
+			ctx.payload.ResponseHeaders[idx].Value = value
+		} else {
+			ctx.payload.ResponseHeaders = append(ctx.payload.ResponseHeaders, &proto.FetchHeaderEntry{
+				Name:  name,
+				Value: value,
+			})
+			headerIndex[name] = len(ctx.payload.ResponseHeaders) - 1
+		}
+	}
+	return ctx
+}
+
+// AddHeader appends key-value pairs to the end of the response headers.
+// Duplicate keys will be preserved.
+func (ctx *HijackResponse) AddHeader(pairs ...string) *HijackResponse {
 	for i := 0; i < len(pairs); i += 2 {
 		ctx.payload.ResponseHeaders = append(ctx.payload.ResponseHeaders, &proto.FetchHeaderEntry{
 			Name:  pairs[i],
diff --git a/hijack_test.go b/hijack_test.go
index a5b114ab..470fd8ce 100644
--- a/hijack_test.go
+++ b/hijack_test.go
@@ -75,6 +75,8 @@ func TestHijack(t *testing.T) {
 		g.Has(ctx.Response.Headers().Get("Content-Type"), "text/html; charset=utf-8")
 
 		// override response header
+		ctx.Response.AddHeader("Set-Cookie", "key=val1")
+		// This should override the previous one
 		ctx.Response.SetHeader("Set-Cookie", "key=val")
 
 		// override response body