diff --git a/lib/phoenix/controller.ex b/lib/phoenix/controller.ex
index 74f1d5bd46..b13ac956dc 100644
--- a/lib/phoenix/controller.ex
+++ b/lib/phoenix/controller.ex
@@ -1094,7 +1094,7 @@ defmodule Phoenix.Controller do
       conn
     else
       content_type = content_type <> "; charset=utf-8"
-      %Plug.Conn{conn | resp_headers: [{"content-type", content_type} | resp_headers]}
+      %{conn | resp_headers: [{"content-type", content_type} | resp_headers]}
     end
   end
 
@@ -1323,7 +1323,7 @@ defmodule Phoenix.Controller do
 
   """
   @spec scrub_params(Plug.Conn.t(), String.t()) :: Plug.Conn.t()
-  def scrub_params(conn, required_key) when is_binary(required_key) do
+  def scrub_params(%Plug.Conn{} = conn, required_key) when is_binary(required_key) do
     param = Map.get(conn.params, required_key) |> scrub_param()
 
     unless param do
@@ -1331,7 +1331,7 @@ defmodule Phoenix.Controller do
     end
 
     params = Map.put(conn.params, required_key, param)
-    %Plug.Conn{conn | params: params}
+    %{conn | params: params}
   end
 
   defp scrub_param(%{__struct__: mod} = struct) when is_atom(mod) do
diff --git a/lib/phoenix/endpoint/render_errors.ex b/lib/phoenix/endpoint/render_errors.ex
index 3400399010..0e0d494bff 100644
--- a/lib/phoenix/endpoint/render_errors.ex
+++ b/lib/phoenix/endpoint/render_errors.ex
@@ -52,12 +52,12 @@ defmodule Phoenix.Endpoint.RenderErrors do
   end
 
   @doc false
-  def __catch__(conn, kind, reason, stack, opts) do
+  def __catch__(%Plug.Conn{} = conn, kind, reason, stack, opts) do
     conn =
       receive do
         @already_sent ->
           send(self(), @already_sent)
-          %Plug.Conn{conn | state: :sent}
+          %{conn | state: :sent}
       after
         0 ->
           instrument_render_and_send(conn, kind, reason, stack, opts)
@@ -126,13 +126,13 @@ defmodule Phoenix.Endpoint.RenderErrors do
     Controller.render(conn, template, assigns)
   end
 
-  defp maybe_fetch_query_params(conn) do
+  defp maybe_fetch_query_params(%Plug.Conn{} = conn) do
     fetch_query_params(conn)
   rescue
     Plug.Conn.InvalidQueryError ->
       case conn.params do
-        %Plug.Conn.Unfetched{} -> %Plug.Conn{conn | query_params: %{}, params: %{}}
-        params -> %Plug.Conn{conn | query_params: %{}, params: params}
+        %Plug.Conn.Unfetched{} -> %{conn | query_params: %{}, params: %{}}
+        params -> %{conn | query_params: %{}, params: params}
       end
   end