diff --git a/lib/ueberauth/strategy/twitter/oauth.ex b/lib/ueberauth/strategy/twitter/oauth.ex
index 7b3ae5b..fb65052 100644
--- a/lib/ueberauth/strategy/twitter/oauth.ex
+++ b/lib/ueberauth/strategy/twitter/oauth.ex
@@ -54,11 +54,14 @@ defmodule Ueberauth.Strategy.Twitter.OAuth do
     config = Application.get_env(:ueberauth, __MODULE__)
 
     @defaults
-    |> Keyword.merge(config)
     |> Keyword.merge(opts)
+    |> Keyword.merge(config, &merge_present_values/3)
     |> Enum.into(%{})
   end
 
+  defp merge_present_values(_key, left, nil), do: left
+  defp merge_present_values(_key, _left, right), do: right
+
   def get(url, access_token), do: get(url, [], access_token)
   def get(url, params, {token, token_secret}) do
     client()
@@ -93,7 +96,7 @@ defmodule Ueberauth.Strategy.Twitter.OAuth do
     {:ok, {token, token_secret}}
   end
 
-  defp decode_response({:ok, %{status_code: status_code, body: %{"errors" => [error | _]}}}) do
+  defp decode_response({:ok, %{body: %{"errors" => [error | _]}}}) do
     {:error, %ApiError{message: error["message"], code: error["code"]}}
   end