diff --git a/runtime/handler.go b/runtime/handler.go
index 2f0b9e9e0f8..4c9083d790f 100644
--- a/runtime/handler.go
+++ b/runtime/handler.go
@@ -28,7 +28,9 @@ func ForwardResponseStream(ctx context.Context, mux *ServeMux, marshaler Marshal
 	}
 	handleForwardResponseServerMetadata(w, mux, md)
 
-	w.Header().Set("Transfer-Encoding", "chunked")
+	if !mux.disableChunkedEncoding {
+		w.Header().Set("Transfer-Encoding", "chunked")
+	}
 	if err := handleForwardResponseOptions(ctx, w, nil, opts); err != nil {
 		HTTPError(ctx, mux, marshaler, w, req, err)
 		return
diff --git a/runtime/handler_test.go b/runtime/handler_test.go
index 42ce5eb13d0..fef8298eff7 100644
--- a/runtime/handler_test.go
+++ b/runtime/handler_test.go
@@ -33,10 +33,11 @@ func TestForwardResponseStream(t *testing.T) {
 		err error
 	}
 	tests := []struct {
-		name         string
-		msgs         []msg
-		statusCode   int
-		responseBody bool
+		name                   string
+		msgs                   []msg
+		statusCode             int
+		responseBody           bool
+		disableChunkedEncoding bool
 	}{{
 		name: "encoding",
 		msgs: []msg{
@@ -74,6 +75,13 @@ func TestForwardResponseStream(t *testing.T) {
 		},
 		responseBody: true,
 		statusCode:   http.StatusOK,
+	}, {
+		name: "disable chunked encoding",
+		msgs: []msg{
+			{&pb.SimpleMessage{Id: "One"}, nil},
+		},
+		statusCode:             http.StatusOK,
+		disableChunkedEncoding: true,
 	}}
 
 	newTestRecv := func(t *testing.T, msgs []msg) func() (proto.Message, error) {
@@ -97,14 +105,24 @@ func TestForwardResponseStream(t *testing.T) {
 			req := httptest.NewRequest("GET", "http://example.com/foo", nil)
 			resp := httptest.NewRecorder()
 
-			runtime.ForwardResponseStream(ctx, runtime.NewServeMux(), marshaler, resp, req, recv)
+			mux := runtime.NewServeMux()
+			if tt.disableChunkedEncoding {
+				mux = runtime.NewServeMux(runtime.WithDisableChunkedEncoding())
+			}
+			runtime.ForwardResponseStream(ctx, mux, marshaler, resp, req, recv)
 
 			w := resp.Result()
 			if w.StatusCode != tt.statusCode {
 				t.Errorf("StatusCode %d want %d", w.StatusCode, tt.statusCode)
 			}
-			if h := w.Header.Get("Transfer-Encoding"); h != "chunked" {
-				t.Errorf("ForwardResponseStream missing header chunked")
+			if !tt.disableChunkedEncoding {
+				if h := w.Header.Get("Transfer-Encoding"); h != "chunked" {
+					t.Errorf("ForwardResponseStream missing header chunked")
+				}
+			} else {
+				if h := w.Header.Get("Transfer-Encoding"); h != "" {
+					t.Errorf("ForwardResponseStream unexpected Transfer-Encoding header %s", h)
+				}
 			}
 			body, err := io.ReadAll(w.Body)
 			if err != nil {
diff --git a/runtime/mux.go b/runtime/mux.go
index 3eb16167173..4e684c7de6c 100644
--- a/runtime/mux.go
+++ b/runtime/mux.go
@@ -73,6 +73,7 @@ type ServeMux struct {
 	disablePathLengthFallback bool
 	unescapingMode            UnescapingMode
 	writeContentLength        bool
+	disableChunkedEncoding    bool
 }
 
 // ServeMuxOption is an option that can be given to a ServeMux on construction.
@@ -125,6 +126,16 @@ func WithMiddlewares(middlewares ...Middleware) ServeMuxOption {
 	}
 }
 
+// WithDisableChunkedEncoding disables the Transfer-Encoding: chunked header
+// for streaming responses. This is useful for streaming implementations that use
+// Content-Length, which is mutually exclusive with Transfer-Encoding:chunked.
+// Note that this option will not automatically add Content-Length headers, so it should be used with caution.
+func WithDisableChunkedEncoding() ServeMuxOption {
+	return func(mux *ServeMux) {
+		mux.disableChunkedEncoding = true
+	}
+}
+
 // SetQueryParameterParser sets the query parameter parser, used to populate message from query parameters.
 // Configuring this will mean the generated OpenAPI output is no longer correct, and it should be
 // done with careful consideration.