diff --git a/lib/http_client_builder.ex b/lib/http_client_builder.ex
index a025788..871fba0 100755
--- a/lib/http_client_builder.ex
+++ b/lib/http_client_builder.ex
@@ -96,8 +96,9 @@ defmodule HttpClientBuilder do
 
         headers =
           if unquote(client_opts)[:runtime_headers_getter] do
-            (unquote(client_opts)[:runtime_headers_getter].() ++ compile_time_headers)
-            |> dedup_headers()
+            compile_time_headers
+            |> Kernel.++(unquote(client_opts)[:runtime_headers_getter].())
+            |> Enum.uniq_by(&elem(&1, 0))
           else
             compile_time_headers
           end
@@ -115,12 +116,6 @@ defmodule HttpClientBuilder do
         base_url <> url_or_path <> query
       end
 
-      defp dedup_headers(headers) do
-        headers
-        |> Enum.reduce(%{}, fn {k, v}, acc -> Map.put(acc, k, v) end)
-        |> Map.to_list()
-      end
-
       defoverridable get: 2, post: 2, put: 2, delete: 2, patch: 2, do_request: 3, build_url: 2
     end
   end