diff --git a/lib/req/steps.ex b/lib/req/steps.ex
index d3defa5..502180c 100644
--- a/lib/req/steps.ex
+++ b/lib/req/steps.ex
@@ -1022,7 +1022,7 @@ defmodule Req.Steps do
       conn =
         Req.Test.Adapter.conn(%Plug.Conn{}, request.method, request.url, req_body)
         |> Map.replace!(:req_headers, req_headers)
-        |> Plug.Conn.fetch_query_params()
+        |> Plug.Conn.fetch_query_params(validate_utf8: false)
         |> Plug.Parsers.call(parser_opts)
 
       # Handle cases where the body isn't read with Plug.Parsers
diff --git a/test/req/steps_test.exs b/test/req/steps_test.exs
index 3bb5281..8fc4ef3 100644
--- a/test/req/steps_test.exs
+++ b/test/req/steps_test.exs
@@ -1875,10 +1875,11 @@ defmodule Req.StepsTest do
       plug = fn conn ->
         {:ok, body, conn} = Plug.Conn.read_body(conn)
         assert body == ~s|{"a":1}|
+        assert conn.query_params == %{"foo" => <<0xFF>>}
         Plug.Conn.send_resp(conn, 200, "ok")
       end
 
-      assert Req.request!(plug: plug, json: %{a: 1}).body == "ok"
+      assert Req.request!(plug: plug, json: %{a: 1}, params: %{foo: <<0xFF>>}).body == "ok"
       refute_receive _
     end