diff --git a/render/data.go b/render/data.go
index a653ea30..2c0ad5e3 100644
--- a/render/data.go
+++ b/render/data.go
@@ -4,7 +4,10 @@
 
 package render
 
-import "net/http"
+import (
+	"net/http"
+	"strconv"
+)
 
 // Data contains ContentType and bytes data.
 type Data struct {
@@ -15,6 +18,9 @@ type Data struct {
 // Render (Data) writes data with custom ContentType.
 func (r Data) Render(w http.ResponseWriter) (err error) {
 	r.WriteContentType(w)
+	if len(r.Data) > 0 {
+		w.Header().Set("Content-Length", strconv.Itoa(len(r.Data)))
+	}
 	_, err = w.Write(r.Data)
 	return
 }
diff --git a/render/render_test.go b/render/render_test.go
index d9ae2067..09ae9f54 100644
--- a/render/render_test.go
+++ b/render/render_test.go
@@ -8,6 +8,7 @@ import (
 	"encoding/xml"
 	"errors"
 	"html/template"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -427,6 +428,36 @@ func TestRenderData(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "#!PNG some raw data", w.Body.String())
 	assert.Equal(t, "image/png", w.Header().Get("Content-Type"))
+	assert.Equal(t, "19", w.Header().Get("Content-Length"))
+}
+
+func TestRenderDataContentLength(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		size, err := strconv.Atoi(r.URL.Query().Get("size"))
+		assert.NoError(t, err)
+
+		data := Data{
+			ContentType: "application/octet-stream",
+			Data:        make([]byte, size),
+		}
+		assert.NoError(t, data.Render(w))
+	}))
+	t.Cleanup(srv.Close)
+
+	for _, size := range []int{0, 1, 100, 100_000} {
+		t.Run(strconv.Itoa(size), func(t *testing.T) {
+			resp, err := http.Get(srv.URL + "?size=" + strconv.Itoa(size))
+			require.NoError(t, err)
+			defer resp.Body.Close()
+
+			assert.Equal(t, "application/octet-stream", resp.Header.Get("Content-Type"))
+			assert.EqualValues(t, strconv.Itoa(size), resp.Header.Get("Content-Length"))
+
+			actual, err := io.Copy(io.Discard, resp.Body)
+			require.NoError(t, err)
+			assert.EqualValues(t, size, actual)
+		})
+	}
 }
 
 func TestRenderString(t *testing.T) {