diff --git a/lib/response.ml b/lib/response.ml
index f6c36682fc..3702ca9874 100644
--- a/lib/response.ml
+++ b/lib/response.ml
@@ -67,18 +67,26 @@ module Make(IO : S.IO) = struct
        let flush = false in
        return (`Ok { encoding; headers; version; status; flush })
 
-  let has_body {status; encoding} =
-    (* rfc7230#section-5.7.1 *)
-    match status with
-    | #Code.informational_status | `No_content | `Not_modified -> `No
-    | #Code.status_code -> Transfer.has_body encoding
+  let allowed_body response = (* rfc7230#section-5.7.1 *)
+    match status response with
+    | #Code.informational_status | `No_content | `Not_modified -> false
+    | #Code.status_code -> true
+
+  let has_body response =
+    if allowed_body response
+    then Transfer.has_body (encoding response)
+    else `No
+
   let make_body_reader {encoding} ic = Transfer_IO.make_reader encoding ic
   let read_body_chunk = Transfer_IO.read
 
   let write_header res oc =
     write oc (Printf.sprintf "%s %s\r\n" (Code.string_of_version res.version)
       (Code.string_of_status res.status)) >>= fun () ->
-    let headers = Header.add_transfer_encoding res.headers res.encoding in
+    let headers =
+      if allowed_body res
+      then Header.add_transfer_encoding res.headers res.encoding
+      else res.headers in
     Header_IO.write headers oc
 
   let make_body_writer ?flush {encoding} oc =
diff --git a/lib_test/test_sanity.ml b/lib_test/test_sanity.ml
index 096cd86662..1a3c7861de 100644
--- a/lib_test/test_sanity.ml
+++ b/lib_test/test_sanity.ml
@@ -1,5 +1,6 @@
 open Lwt
 open OUnit
+open Cohttp
 open Cohttp_lwt_unix
 open Cohttp_lwt_unix_test
 
@@ -57,6 +58,9 @@ let ts =
     let not_modified_has_no_body () =
       Client.get uri >>= fun (resp, body) ->
       assert_equal (Response.status resp) `Not_modified;
+      let headers = Response.headers resp in
+      assert_equal ~printer:Transfer.string_of_encoding
+        Transfer.Unknown (Header.get_transfer_encoding headers);
       body |> Body.is_empty >|= fun is_empty ->
       assert_bool "No body returned when not modified" is_empty in
     [ "sanity test", t
diff --git a/lwt/cohttp_lwt.ml b/lwt/cohttp_lwt.ml
index 81c0243ddc..1d07a291b7 100644
--- a/lwt/cohttp_lwt.ml
+++ b/lwt/cohttp_lwt.ml
@@ -310,7 +310,7 @@ module Make_server(IO:IO) = struct
     Filename.concat docroot rel_path
 
   let respond ?headers ?(flush=true) ~status ~body () =
-    let encoding = 
+    let encoding =
       match headers with
       | None -> Cohttp_lwt_body.transfer_encoding body
       | Some headers ->