diff --git a/lib/phoenix/controller.ex b/lib/phoenix/controller.ex
index 95cb139e5e..74f1d5bd46 100644
--- a/lib/phoenix/controller.ex
+++ b/lib/phoenix/controller.ex
@@ -1274,7 +1274,7 @@ defmodule Phoenix.Controller do
   end
 
   defp encode_filename(filename, false), do: filename
-  defp encode_filename(filename, true), do: URI.encode(filename)
+  defp encode_filename(filename, true), do: URI.encode(filename, &URI.char_unreserved?/1)
 
   defp get_disposition_type(:attachment), do: "attachment"
   defp get_disposition_type(:inline), do: "inline"
diff --git a/test/phoenix/controller/controller_test.exs b/test/phoenix/controller/controller_test.exs
index 279715fa72..4b2057f09c 100644
--- a/test/phoenix/controller/controller_test.exs
+++ b/test/phoenix/controller/controller_test.exs
@@ -537,6 +537,17 @@ defmodule Phoenix.Controller.ControllerTest do
              "world"
     end
 
+    test "sends file for download for filename with unreserved characters" do
+      conn = send_download(conn(:get, "/"), {:file, @hello_txt}, filename: "hello, world.json")
+      assert conn.status == 200
+      assert get_resp_header(conn, "content-disposition") ==
+             ["attachment; filename=\"hello%2C%20world.json\"; filename*=utf-8''hello%2C%20world.json"]
+      assert get_resp_header(conn, "content-type") ==
+             ["application/json"]
+      assert conn.resp_body ==
+             "world"
+    end
+
     test "sends file supports UTF-8" do
       conn = send_download(conn(:get, "/"), {:file, @hello_txt}, filename: "测 试.txt")
       assert conn.status == 200