diff --git a/changelog.d/fix-preferred-frontend.fix b/changelog.d/fix-preferred-frontend.fix
new file mode 100644
index 000000000..07bf4d0c6
--- /dev/null
+++ b/changelog.d/fix-preferred-frontend.fix
@@ -0,0 +1 @@
+Fix preferred frontend not working due to InstanceStatic plug prematurely returning HTTP 404
diff --git a/lib/pleroma/web/endpoint.ex b/lib/pleroma/web/endpoint.ex
index 07b33f866..8552f5d0a 100644
--- a/lib/pleroma/web/endpoint.ex
+++ b/lib/pleroma/web/endpoint.ex
@@ -139,6 +139,8 @@ defmodule Pleroma.Web.Endpoint do
     from: {:pleroma, "priv/static/adminfe/"}
   )
 
+  plug(Pleroma.Web.Plugs.StaticNotFoundPlug)
+
   # Code reloading can be explicitly enabled under the
   # :code_reloader configuration of your endpoint.
   if code_reloading? do
diff --git a/lib/pleroma/web/plugs/ensure_host_matches_plug.ex b/lib/pleroma/web/plugs/ensure_host_matches_plug.ex
index ab2129f9e..960e86d4f 100644
--- a/lib/pleroma/web/plugs/ensure_host_matches_plug.ex
+++ b/lib/pleroma/web/plugs/ensure_host_matches_plug.ex
@@ -4,6 +4,7 @@
 
 defmodule Pleroma.Web.Plugs.EnsureHostMatchesPlug do
   @moduledoc "Ensures Host header matches instance"
+  @behaviour Plug
 
   alias Pleroma.Web.Endpoint
 
diff --git a/lib/pleroma/web/plugs/instance_static.ex b/lib/pleroma/web/plugs/instance_static.ex
index 948188287..d2a674d39 100644
--- a/lib/pleroma/web/plugs/instance_static.ex
+++ b/lib/pleroma/web/plugs/instance_static.ex
@@ -4,7 +4,7 @@
 
 defmodule Pleroma.Web.Plugs.InstanceStatic do
   require Pleroma.Constants
-  import Plug.Conn, only: [put_resp_header: 3, put_status: 2, send_resp: 3, halt: 1]
+  import Plug.Conn, only: [put_resp_header: 3]
 
   @moduledoc """
   This is a shim to call `Plug.Static` but with runtime `from` configuration.
@@ -51,37 +51,10 @@ defmodule Pleroma.Web.Plugs.InstanceStatic do
       |> Map.put(:from, from)
       |> Map.put(:content_types, false)
 
-    conn =
-      conn
-      |> set_content_type(conn.request_path)
-      |> Plug.Static.call(opts)
+    conn = set_content_type(conn, conn.request_path)
 
-    if conn.halted do
-      conn
-    else
-      path = String.trim_leading(conn.request_path, "/")
-
-      if not File.exists?(file_path(path)) do
-        conn
-        |> put_status(:not_found)
-        |> send_404()
-        |> halt()
-      else
-        conn
-      end
-    end
-  end
-
-  defp send_404(conn) do
-    if String.ends_with?(String.downcase(conn.request_path), ".json") do
-      conn
-      |> put_resp_header("content-type", "application/json")
-      |> send_resp(404, Jason.encode!(%{error: "not found"}))
-    else
-      conn
-      |> put_resp_header("content-type", "text/plain")
-      |> send_resp(404, "Not found")
-    end
+    # Call Plug.Static with our sanitized content-type
+    Plug.Static.call(conn, opts)
   end
 
   defp set_content_type(conn, "/emoji/" <> filepath) do
diff --git a/lib/pleroma/web/plugs/static_not_found_plug.ex b/lib/pleroma/web/plugs/static_not_found_plug.ex
new file mode 100644
index 000000000..e2e7a622c
--- /dev/null
+++ b/lib/pleroma/web/plugs/static_not_found_plug.ex
@@ -0,0 +1,38 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2026 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Plugs.StaticNotFoundPlug do
+  @moduledoc """
+  A small plug that enforces returning 404 on static files when they don't exist.
+  """
+  @behaviour Plug
+
+  require Pleroma.Constants
+  import Plug.Conn, only: [put_resp_header: 3, send_resp: 3, halt: 1]
+
+  def init(opts), do: opts
+
+  for only <- Pleroma.Constants.static_only_files() do
+    def call(%{request_path: "/" <> unquote(only) <> _} = conn, _opts) do
+      send_404(conn)
+    end
+  end
+
+  def call(conn, _) do
+    conn
+  end
+
+  defp send_404(conn) do
+    if String.ends_with?(String.downcase(conn.request_path), ".json") do
+      conn
+      |> put_resp_header("content-type", "application/json")
+      |> send_resp(404, Jason.encode!(%{error: "not found"}))
+    else
+      conn
+      |> put_resp_header("content-type", "text/plain")
+      |> send_resp(404, "Not found")
+    end
+    |> halt()
+  end
+end
diff --git a/test/pleroma/web/plugs/frontend_static_plug_test.exs b/test/pleroma/web/plugs/frontend_static_plug_test.exs
index b7c06eacd..7dc7e52cf 100644
--- a/test/pleroma/web/plugs/frontend_static_plug_test.exs
+++ b/test/pleroma/web/plugs/frontend_static_plug_test.exs
@@ -122,16 +122,27 @@ defmodule Pleroma.Web.Plugs.FrontendStaticPlugTest do
 
       clear_config([:frontends, :pickable], ["#{name}/#{ref}"])
       path = "#{@dir}/frontends/#{name}/#{ref}"
+      path2 = "#{@dir}/frontends/#{name}/#{ref}/packs/html"
 
       Pleroma.Backports.mkdir_p!(path)
       File.write!("#{path}/index.html", "from frontend plug")
 
+      Pleroma.Backports.mkdir_p!(path2)
+      File.write!("#{path2}/custom.html", "from frontend plug")
+
       index =
         conn
         |> put_req_cookie("preferred_frontend", "#{name}/#{ref}")
         |> get("/")
 
       assert html_response(index, 200) == "from frontend plug"
+
+      custom =
+        conn
+        |> put_req_cookie("preferred_frontend", "#{name}/#{ref}")
+        |> get("/packs/html/custom.html")
+
+      assert html_response(custom, 200) == "from frontend plug"
     end
 
     test "only returns content from pickable frontends", %{conn: conn} do
diff --git a/test/pleroma/web/plugs/instance_static_test.exs b/test/pleroma/web/plugs/instance_static_test.exs
index 017c49d1e..1d67e8dc3 100644
--- a/test/pleroma/web/plugs/instance_static_test.exs
+++ b/test/pleroma/web/plugs/instance_static_test.exs
@@ -61,6 +61,28 @@ defmodule Pleroma.Web.Plugs.InstanceStaticTest do
     File.write!(@dir <> "/static/kaniini.html", "<h1>rabbit hugs as a service</h1>")
     index = get(build_conn(), "/static/kaniini.html")
     assert html_response(index, 200) == "<h1>rabbit hugs as a service</h1>"
+
+    File.write!(@dir <> "/static/kaniini the bnuuy.html", "<h1>rabbit hugs as a service</h1>")
+    index = get(build_conn(), "/static/kaniini%20the%20bnuuy.html")
+    assert html_response(index, 200) == "<h1>rabbit hugs as a service</h1>"
+  end
+
+  test "overrides /static/styles files with spaces in URL" do
+    Pleroma.Backports.mkdir_p!(@dir <> "/static/styles")
+    File.write(@dir <> "/static/styles/Redmond DX.iss", "overridden")
+
+    index = get(build_conn(), "/static/styles/Redmond%20DX.iss")
+    assert index.status == 200
+    assert index.resp_body == File.read!(@dir <> "/static/styles/Redmond DX.iss")
+    assert index.halted == true
+  end
+
+  test "serves fallback /static/styles files with spaces in URL" do
+    index = get(build_conn(), "/static/styles/Redmond%20DX.iss")
+
+    assert index.status == 200
+    assert index.resp_body == File.read!("priv/static/static/styles/Redmond DX.iss")
+    assert index.halted == true
   end
 
   test "does not sanitize dangerous files in general, as there can be html and javascript files legitimately in this folder" do
@@ -137,47 +159,4 @@ defmodule Pleroma.Web.Plugs.InstanceStaticTest do
     # It should be preserved because "image" is in the allowed_mime_types list
     assert content_type == "image/jpeg"
   end
-
-  describe "404s for missing files in static-only paths" do
-    test "returns 404 for non-existent static-only JSON files" do
-      conn = get(build_conn(), "/static/non-existent.json")
-
-      assert conn.status == 404
-      assert ["application/json"] = get_resp_header(conn, "content-type")
-      assert Jason.decode!(conn.resp_body) == %{"error" => "not found"}
-    end
-
-    test "returns 404 for non-existent static-only non-JSON files" do
-      conn = get(build_conn(), "/static/non-existent.txt")
-
-      assert conn.status == 404
-      assert conn.resp_body == "Not found"
-      assert ["text/plain"] = get_resp_header(conn, "content-type")
-    end
-
-    test "returns 404 for non-existent .css files" do
-      conn = get(build_conn(), "/static/non-existent.css")
-
-      assert conn.status == 404
-      assert conn.resp_body == "Not found"
-      # Verifies that we forced text/plain for the error body, even though the path was .css
-      assert ["text/plain"] = get_resp_header(conn, "content-type")
-    end
-
-    test "returns 404 for non-existent files without an extension" do
-      conn = get(build_conn(), "/static/non-existent")
-
-      assert conn.status == 404
-      assert conn.resp_body == "Not found"
-      assert ["text/plain"] = get_resp_header(conn, "content-type")
-    end
-
-    test "returns 200 (falls through to SPA) for non-static-only paths" do
-      # /some-route is NOT in static_only_files, so it should still fall through to the SPA.
-      conn = get(build_conn(), "/some-route")
-
-      assert conn.status == 200
-      assert ["text/html; charset=utf-8"] = get_resp_header(conn, "content-type")
-    end
-  end
 end
diff --git a/test/pleroma/web/plugs/static_not_found_plug_test.exs b/test/pleroma/web/plugs/static_not_found_plug_test.exs
new file mode 100644
index 000000000..a5d063c53
--- /dev/null
+++ b/test/pleroma/web/plugs/static_not_found_plug_test.exs
@@ -0,0 +1,49 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2026 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+defmodule Pleroma.Web.Plugs.StaticNotFoundPlugTest do
+  use Pleroma.Web.ConnCase
+
+  describe "404s for missing files in static-only paths" do
+    test "returns 404 for non-existent static-only JSON files" do
+      conn = get(build_conn(), "/static/non-existent.json")
+
+      assert conn.status == 404
+      assert ["application/json"] = get_resp_header(conn, "content-type")
+      assert Jason.decode!(conn.resp_body) == %{"error" => "not found"}
+    end
+
+    test "returns 404 for non-existent static-only non-JSON files" do
+      conn = get(build_conn(), "/static/non-existent.txt")
+
+      assert conn.status == 404
+      assert conn.resp_body == "Not found"
+      assert ["text/plain"] = get_resp_header(conn, "content-type")
+    end
+
+    test "returns 404 for non-existent .css files" do
+      conn = get(build_conn(), "/static/non-existent.css")
+
+      assert conn.status == 404
+      assert conn.resp_body == "Not found"
+      # Verifies that we forced text/plain for the error body, even though the path was .css
+      assert ["text/plain"] = get_resp_header(conn, "content-type")
+    end
+
+    test "returns 404 for non-existent files without an extension" do
+      conn = get(build_conn(), "/static/non-existent")
+
+      assert conn.status == 404
+      assert conn.resp_body == "Not found"
+      assert ["text/plain"] = get_resp_header(conn, "content-type")
+    end
+
+    test "returns 200 (falls through to SPA) for non-static-only paths" do
+      # /some-route is NOT in static_only_files, so it should still fall through to the SPA.
+      conn = get(build_conn(), "/some-route")
+
+      assert conn.status == 200
+      assert ["text/html; charset=utf-8"] = get_resp_header(conn, "content-type")
+    end
+  end
+end