diff --git a/src/e9p_fs.erl b/src/e9p_fs.erl
index 725125a..8ebc860 100644
--- a/src/e9p_fs.erl
+++ b/src/e9p_fs.erl
@@ -109,7 +109,6 @@
 -record(state, {
     mod,
     state,
-    version,
     fids = #{},
     max_packet_size
 }).
@@ -132,9 +131,9 @@ init(Mod, State) ->
     end.
 
 negotiate(#state{} = State, ~"9P2000", MPS) ->
-    {ok, State#state{version = legacy, max_packet_size = MPS}};
+    {ok, legacy, State#state{max_packet_size = MPS}};
 negotiate(#state{} = State, ~"9P2000.u", MPS) ->
-    {ok, State#state{version = unix, max_packet_size = MPS}};
+    {ok, unix, State#state{max_packet_size = MPS}};
 negotiate(#state{} = State, _Other, _MPS) ->
     {error, ~"Unsupported version", State}.
 
diff --git a/src/e9p_msg.erl b/src/e9p_msg.erl
index 573b7d7..fbe6bd1 100644
--- a/src/e9p_msg.erl
+++ b/src/e9p_msg.erl
@@ -288,10 +288,10 @@ do_encode(#tclunk{fid = FID}, _Ver) ->
     {?Tclunk, <<FID:4/?int>>};
 do_encode(#rclunk{}, _Ver) ->
     {?Rclunk, []};
-do_encode(#rerror{msg = Error}, legacy) ->
-    {?Rerror, encode_str(Error)};
-do_encode(#rerror{msg = Error, errno = Errno}, _Ver) ->
+do_encode(#rerror{msg = Error, errno = Errno}, unix) ->
     {?Rerror, [encode_str(Error), <<Errno:4/?int>>]};
+do_encode(#rerror{msg = Error}, _Version) ->
+    {?Rerror, encode_str(Error)};
 do_encode(#tflush{tag = Tag}, _Ver) ->
     {?Tflush, <<Tag:2/?int>>};
 do_encode(#rflush{}, _Ver) ->
diff --git a/src/e9p_server.erl b/src/e9p_server.erl
index b524f56..f601013 100644
--- a/src/e9p_server.erl
+++ b/src/e9p_server.erl
@@ -22,7 +22,8 @@
 -record(state, {
     socket,
     % trans_mod = gen_tcp,
-    handler
+    handler,
+    version
 }).
 
 start(Port, Handler) ->
@@ -64,10 +65,18 @@ loop(#state{socket = Sock} = State) ->
         {ok, Tag, Data} ->
             try handle_message(Data, State) of
                 {ok, Reply, NewState} ->
-                    e9p_transport:send(Sock, Tag, Reply),
+                    ?LOG_DEBUG(#{
+                        tag => Tag, req => Data, reply => Reply, state => NewState, pid => self()
+                    }),
+                    e9p_transport:send(Sock, Tag, Reply, NewState#state.version),
                     ?MODULE:loop(NewState);
                 {error, Err, RHandler} ->
-                    e9p_transport:send(Sock, Tag, #rerror{msg = Err}),
+                    e9p_transport:send(
+                        Sock,
+                        Tag,
+                        #rerror{msg = Err},
+                        State#state.version
+                    ),
                     ?MODULE:loop(State#state{handler = RHandler})
             catch
                 C:E:S ->
@@ -76,9 +85,14 @@ loop(#state{socket = Sock} = State) ->
                         msg => E,
                         stacktrace => S
                     }),
-                    e9p_transport:send(Sock, Tag, #rerror{
-                        msg = io_lib:format("Caught ~p: ~p", [C, E])
-                    }),
+                    e9p_transport:send(
+                        Sock,
+                        Tag,
+                        #rerror{
+                            msg = io_lib:format("Caught ~p: ~p", [C, E])
+                        },
+                        State#state.version
+                    ),
                     ?MODULE:loop(State)
             end;
         {error, closed} ->
@@ -103,8 +117,8 @@ do_cast(#state{handler = Handler} = State, Func, Args) ->
 
 handle_message(#tversion{version = Version, max_packet_size = MPS}, State) ->
     maybe
-        {ok, NewState} ?= do_cast(State, negotiate, [Version, MPS]),
-        {ok, #rversion{version = Version, max_packet_size = MPS}, NewState}
+        {ok, Ver, NewState} ?= do_call(State, negotiate, [Version, MPS]),
+        {ok, #rversion{version = Version, max_packet_size = MPS}, NewState#state{version = Ver}}
     end;
 handle_message(#tflush{}, State) ->
     % Currently there is no support for parallel messages, so this does simply
diff --git a/src/e9p_transport.erl b/src/e9p_transport.erl
index 3994a64..2c90803 100644
--- a/src/e9p_transport.erl
+++ b/src/e9p_transport.erl
@@ -8,10 +8,10 @@
 
 % -include_lib("kernel/include/logger.hrl").
 
--export([send/3, read/1, read_stream/1]).
+-export([send/4, read/1, read_stream/1]).
 
-send(Socket, Tag, Message) ->
-    Encoded = e9p_msg:encode(Tag, Message),
+send(Socket, Tag, Message, Version) ->
+    Encoded = e9p_msg:encode(Tag, Message, Version),
     Size = iolist_size(Encoded) + 4,
     gen_tcp:send(Socket, [<<Size:4/?int>>, Encoded]).