diff --git a/changelog.d/mastodon-websocket-protocol.fix b/changelog.d/mastodon-websocket-protocol.fix
new file mode 100644
index 000000000..66dab16ed
--- /dev/null
+++ b/changelog.d/mastodon-websocket-protocol.fix
@@ -0,0 +1 @@
+Echo Mastodon-style `Sec-WebSocket-Protocol` tokens in streaming WebSocket handshakes.
diff --git a/lib/pleroma/web/endpoint.ex b/lib/pleroma/web/endpoint.ex
index 36e78e1e2..07b33f866 100644
--- a/lib/pleroma/web/endpoint.ex
+++ b/lib/pleroma/web/endpoint.ex
@@ -9,8 +9,8 @@ defmodule Pleroma.Web.Endpoint do
 
   alias Pleroma.Config
 
-  socket("/api/v1/streaming", Pleroma.Web.MastodonAPI.WebsocketHandler,
-    longpoll: false,
+  plug(Pleroma.Web.MastodonAPI.WebsocketPlug,
+    path: "/api/v1/streaming",
     websocket: [
       path: "/",
       compress: false,
@@ -169,8 +169,7 @@ defmodule Pleroma.Web.Endpoint do
       else: "pleroma_key"
 
   extra =
-    Config.get([__MODULE__, :extra_cookie_attrs])
-    |> Enum.join(";")
+    Enum.join(Config.get([__MODULE__, :extra_cookie_attrs]), ";")
 
   # The session will be stored in the cookie and signed,
   # this means its contents can be read but not tampered with.
diff --git a/lib/pleroma/web/mastodon_api/websocket_handler.ex b/lib/pleroma/web/mastodon_api/websocket_handler.ex
index 2b698bd5d..3dc862a5a 100644
--- a/lib/pleroma/web/mastodon_api/websocket_handler.ex
+++ b/lib/pleroma/web/mastodon_api/websocket_handler.ex
@@ -67,9 +67,10 @@ defmodule Pleroma.Web.MastodonAPI.WebsocketHandler do
 
   @impl Phoenix.Socket.Transport
   def handle_in({text, [opcode: :text]}, state) do
-    with {:ok, %{} = event} <- Jason.decode(text) do
-      handle_client_event(event, state)
-    else
+    case Jason.decode(text) do
+      {:ok, %{} = event} ->
+        handle_client_event(event, state)
+
       _ ->
         Logger.error("#{__MODULE__} received non-JSON event: #{inspect(text)}")
         {:ok, state}
@@ -85,11 +86,11 @@ defmodule Pleroma.Web.MastodonAPI.WebsocketHandler do
   def handle_info({:render_with_user, view, template, item, topic}, state) do
     user = %User{} = User.get_cached_by_ap_id(state.user.ap_id)
 
-    unless Streamer.filtered_by_user?(user, item) do
+    if Streamer.filtered_by_user?(user, item) do
+      {:ok, state}
+    else
       message = view.render(template, item, user, topic)
       {:push, {:text, message}, %{state | user: user}}
-    else
-      {:ok, state}
     end
   end
 
@@ -253,7 +254,7 @@ defmodule Pleroma.Web.MastodonAPI.WebsocketHandler do
 
   defp find_sec_websocket_protocol(sec_headers) do
     Enum.find_value(sec_headers, fn
-      {"sec-websocket-protocol", token} -> token
+      {"sec-websocket-protocol", protocols} -> protocols |> Plug.Conn.Utils.list() |> List.first()
       _ -> nil
     end)
   end
diff --git a/lib/pleroma/web/mastodon_api/websocket_plug.ex b/lib/pleroma/web/mastodon_api/websocket_plug.ex
new file mode 100644
index 000000000..58ee913b4
--- /dev/null
+++ b/lib/pleroma/web/mastodon_api/websocket_plug.ex
@@ -0,0 +1,105 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.MastodonAPI.WebsocketPlug do
+  @moduledoc """
+  A Phoenix 1.8 compatible WebSocket transport for Mastodon streaming.
+
+  It mirrors Phoenix.Transports.WebSocket, but echoes a successfully authenticated
+  Mastodon-style Sec-WebSocket-Protocol token so browser clients accept the handshake.
+  """
+
+  @behaviour Plug
+
+  import Plug.Conn
+
+  alias Phoenix.Socket.Transport
+  alias Pleroma.Web.Endpoint
+  alias Pleroma.Web.MastodonAPI.WebsocketHandler
+
+  @connect_info_opts [:check_csrf]
+
+  @impl Plug
+  def init(opts) do
+    path = String.split(Keyword.fetch!(opts, :path), "/", trim: true)
+    websocket = Keyword.fetch!(opts, :websocket)
+    config = Transport.load_config(websocket, Phoenix.Transports.WebSocket)
+
+    {path, config}
+  end
+
+  @impl Plug
+  def call(%{method: "GET", path_info: path} = conn, {path, opts}) do
+    conn
+    |> fetch_query_params()
+    |> Transport.code_reload(Endpoint, opts)
+    |> Transport.transport_log(opts[:transport_log])
+    |> Transport.check_origin(WebsocketHandler, Endpoint, opts)
+    |> connect(opts)
+  end
+
+  def call(%{path_info: path} = conn, {path, _opts}) do
+    conn
+    |> send_resp(400, "")
+    |> halt()
+  end
+
+  def call(conn, _opts), do: conn
+
+  defp connect(%{halted: true} = conn, _opts), do: conn
+
+  defp connect(%{params: params} = conn, opts) do
+    keys = Keyword.get(opts, :connect_info, [])
+
+    connect_info =
+      Transport.connect_info(conn, Endpoint, keys, Keyword.take(opts, @connect_info_opts))
+
+    config = %{
+      endpoint: Endpoint,
+      transport: :websocket,
+      options: opts,
+      params: params,
+      connect_info: connect_info
+    }
+
+    case WebsocketHandler.connect(config) do
+      {:ok, arg} ->
+        try do
+          conn
+          |> echo_sec_websocket_protocol()
+          |> WebSockAdapter.upgrade(WebsocketHandler, arg, opts)
+          |> halt()
+        rescue
+          e in WebSockAdapter.UpgradeError ->
+            conn
+            |> send_resp(400, e.message)
+            |> halt()
+        end
+
+      :error ->
+        conn
+        |> send_resp(403, "")
+        |> halt()
+
+      {:error, reason} ->
+        {m, f, args} = opts[:error_handler]
+
+        halt(apply(m, f, [conn, reason | args]))
+    end
+  end
+
+  defp echo_sec_websocket_protocol(conn) do
+    case get_req_header(conn, "sec-websocket-protocol") do
+      [protocols | _] ->
+        case Plug.Conn.Utils.list(protocols) do
+          [protocol | _] -> put_resp_header(conn, "sec-websocket-protocol", protocol)
+          nil -> conn
+          [] -> conn
+        end
+
+      [] ->
+        conn
+    end
+  end
+end
diff --git a/test/pleroma/integration/mastodon_websocket_test.exs b/test/pleroma/integration/mastodon_websocket_test.exs
index 078bb643c..de88e5002 100644
--- a/test/pleroma/integration/mastodon_websocket_test.exs
+++ b/test/pleroma/integration/mastodon_websocket_test.exs
@@ -11,6 +11,7 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
 
   alias Pleroma.Integration.WebsocketClient
   alias Pleroma.Web.CommonAPI
+  alias Pleroma.Web.MastodonAPI.StatusView
   alias Pleroma.Web.OAuth
 
   @moduletag needs_streamer: true, capture_log: true
@@ -31,6 +32,48 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
     WebsocketClient.start_link(self(), path, headers)
   end
 
+  defp raw_websocket_handshake(qs, headers) do
+    uri = URI.parse(@path <> qs)
+    port = uri.port || 80
+    path = uri.path <> if(uri.query, do: "?" <> uri.query, else: "")
+
+    default_headers = [
+      {"host", "#{uri.host}:#{port}"},
+      {"upgrade", "websocket"},
+      {"connection", "Upgrade"},
+      {"sec-websocket-key", Base.encode64(:crypto.strong_rand_bytes(16))},
+      {"sec-websocket-version", "13"}
+    ]
+
+    request = [
+      "GET #{path} HTTP/1.1\r\n",
+      Enum.map(default_headers ++ headers, fn {name, value} -> "#{name}: #{value}\r\n" end),
+      "\r\n"
+    ]
+
+    with {:ok, socket} <-
+           :gen_tcp.connect(String.to_charlist(uri.host), port, [:binary, active: false], 1_000),
+         :ok <- :gen_tcp.send(socket, request),
+         {:ok, response} <- :gen_tcp.recv(socket, 0, 1_000) do
+      :gen_tcp.close(socket)
+      {:ok, parse_http_response(response)}
+    end
+  end
+
+  defp parse_http_response(response) do
+    [headers | _] = String.split(response, "\r\n\r\n", parts: 2)
+    [status_line | header_lines] = String.split(headers, "\r\n")
+    [_, status | _] = String.split(status_line, " ")
+
+    headers =
+      Enum.map(header_lines, fn line ->
+        [name, value] = String.split(line, ":", parts: 2)
+        {String.downcase(name), String.trim(value)}
+      end)
+
+    %{status: String.to_integer(status), headers: headers}
+  end
+
   defp decode_json(json) do
     with {:ok, %{"event" => event, "payload" => payload_text}} <- Jason.decode(json),
          {:ok, payload} <- Jason.decode(payload_text) do
@@ -85,9 +128,7 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
     assert json["payload"]
     assert {:ok, json} = Jason.decode(json["payload"])
 
-    view_json =
-      Pleroma.Web.MastodonAPI.StatusView.render("show.json", activity: activity, for: nil)
-      |> atom_key_to_string()
+    view_json = atom_key_to_string(StatusView.render("show.json", activity: activity, for: nil))
 
     assert json == view_json
   end
@@ -114,10 +155,7 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
       assert json["payload"]
       assert {:ok, json} = Jason.decode(json["payload"])
 
-      view_json =
-        Pleroma.Web.MastodonAPI.StatusView.render("show.json", activity: activity, for: nil)
-        |> Jason.encode!()
-        |> Jason.decode!()
+      view_json = atom_key_to_string(StatusView.render("show.json", activity: activity, for: nil))
 
       assert json == view_json
     end
@@ -279,6 +317,34 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
       end)
     end
 
+    test "echoes the Sec-WebSocket-Protocol token in the handshake", %{token: token} do
+      assert {:ok, %{status: 101, headers: headers}} =
+               raw_websocket_handshake("?stream=user", [
+                 {"sec-websocket-protocol", token.token}
+               ])
+
+      assert {"sec-websocket-protocol", token.token} in headers
+    end
+
+    test "echoes the selected Sec-WebSocket-Protocol token", %{token: token} do
+      assert {:ok, %{status: 101, headers: headers}} =
+               raw_websocket_handshake("?stream=user", [
+                 {"sec-websocket-protocol", "#{token.token}, phoenix"}
+               ])
+
+      assert {"sec-websocket-protocol", token.token} in headers
+    end
+
+    test "does not echo an invalid Sec-WebSocket-Protocol token", %{token: token} do
+      assert {:ok, %{status: 401, headers: headers}} =
+               raw_websocket_handshake("?stream=user", [
+                 {"sec-websocket-protocol", "invalid"}
+               ])
+
+      refute {"sec-websocket-protocol", token.token} in headers
+      refute List.keymember?(headers, "sec-websocket-protocol", 0)
+    end
+
     test "prefers sec-websocket-protocol token over query access_token", %{
       token: token,
       user: user
@@ -450,12 +516,12 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
       assert {:ok, json} = Jason.decode(json["payload"])
 
       view_json =
-        Pleroma.Web.MastodonAPI.StatusView.render("show.json",
-          activity: activity,
-          for: reading_user
+        atom_key_to_string(
+          StatusView.render("show.json",
+            activity: activity,
+            for: reading_user
+          )
         )
-        |> Jason.encode!()
-        |> Jason.decode!()
 
       assert json == view_json
     end
@@ -478,12 +544,12 @@ defmodule Pleroma.Integration.MastodonWebsocketTest do
       activity = Pleroma.Activity.normalize(activity)
 
       view_json =
-        Pleroma.Web.MastodonAPI.StatusView.render("show.json",
-          activity: activity,
-          for: reading_user
+        atom_key_to_string(
+          StatusView.render("show.json",
+            activity: activity,
+            for: reading_user
+          )
         )
-        |> Jason.encode!()
-        |> Jason.decode!()
 
       assert {:ok, %{"event" => "status.update", "payload" => ^view_json}} = decode_json(raw_json)
     end