diff --git a/lib/protobuf/decoder.ex b/lib/protobuf/decoder.ex
index b8609c76..7dbacf11 100644
--- a/lib/protobuf/decoder.ex
+++ b/lib/protobuf/decoder.ex
@@ -15,8 +15,7 @@ defmodule Protobuf.Decoder do
 
     bin
     |> build_message(struct(module), props)
-    |> reverse_repeated(repeated_fields)
-    |> Map.update!(:__unknown_fields__, &Enum.reverse/1)
+    |> reverse_repeated([:__unknown_fields__ | repeated_fields])
     |> transform_module(module)
   end
 
@@ -173,12 +172,12 @@ defmodule Protobuf.Decoder do
   defp handle_value(<<rest::bits>>, field_number, wire_type, value, message, props) do
     case props.field_props do
       %{^field_number => %FieldProps{packed?: true, name_atom: name_atom} = prop} ->
-        new_message = update_in_message(message, name_atom, &value_for_packed(value, &1, prop))
+        new_message = update_in_message(message, name_atom, value, &value_for_packed/3, prop)
         build_message(rest, new_message, props)
 
       %{^field_number => %FieldProps{wire_type: ^wire_type} = prop} ->
         key = field_key(prop, props)
-        new_message = update_in_message(message, key, &value_for_field(value, &1, prop))
+        new_message = update_in_message(message, key, value, &value_for_field/3, prop)
         build_message(rest, new_message, props)
 
       # Repeated fields of primitive numeric types can be "packed". Their packed? flag will be
@@ -187,7 +186,7 @@ defmodule Protobuf.Decoder do
       # https://developers.google.com/protocol-buffers/docs/encoding#packed
       %{^field_number => %FieldProps{repeated?: true, name_atom: name_atom} = prop}
       when wire_type == wire_delimited() ->
-        new_message = update_in_message(message, name_atom, &value_for_packed(value, &1, prop))
+        new_message = update_in_message(message, name_atom, value, &value_for_packed/3, prop)
         build_message(rest, new_message, props)
 
       %{^field_number => %FieldProps{wire_type: expected, name: field}} ->
@@ -374,16 +373,21 @@ defmodule Protobuf.Decoder do
 
   defp decode_fixed64(<<>>, _type, acc), do: acc
 
-  defp reverse_repeated(message, repeated_fields) do
-    Enum.reduce(repeated_fields, message, fn repeated_field, message_acc ->
-      case message_acc do
-        %{^repeated_field => values} when is_list(values) ->
-          %{message_acc | repeated_field => Enum.reverse(values)}
+  defp reverse_repeated(message, [repeated_field | rest]) do
+    message =
+      case message do
+        %{^repeated_field => [_, _ | _] = values} ->
+          %{message | repeated_field => Enum.reverse(values)}
 
         _other ->
-          message_acc
+          message
       end
-    end)
+
+    reverse_repeated(message, rest)
+  end
+
+  defp reverse_repeated(message, []) do
+    message
   end
 
   defp field_key(%FieldProps{oneof: nil, name_atom: key}, _message_props) do
@@ -395,13 +399,16 @@ defmodule Protobuf.Decoder do
     key
   end
 
-  defp update_in_message(message, key, update_fun) do
+  # Receives an update_fun and calls it with value and props params to avoid
+  # the extra memory usage of creating an anonymous function with the two
+  # two params in it's context
+  defp update_in_message(message, key, value, update_fun, props) do
     current =
       case message do
         %_{^key => value} -> value
         %_{} -> nil
       end
 
-    Map.put(message, key, update_fun.(current))
+    Map.put(message, key, update_fun.(value, current, props))
   end
 end