diff --git a/src/machi_pb_high_client.erl b/src/machi_pb_high_client.erl
index ef1e740..18dcc34 100644
--- a/src/machi_pb_high_client.erl
+++ b/src/machi_pb_high_client.erl
@@ -38,7 +38,7 @@
          connected_p/1,
          echo/2, echo/3,
          auth/3, auth/4,
-         append_chunk/6, append_chunk/7,
+         append_chunk/7, append_chunk/8,
          write_chunk/5, write_chunk/6,
          read_chunk/5, read_chunk/6,
          trim_chunk/4, trim_chunk/5,
@@ -96,21 +96,21 @@ auth(PidSpec, User, Pass) ->
 auth(PidSpec, User, Pass, Timeout) ->
     send_sync(PidSpec, {auth, User, Pass}, Timeout).
 
--spec append_chunk(pid(), PlacementKey::binary(), Prefix::binary(), Chunk::binary(),
+-spec append_chunk(pid(), CoC_namespace::binary(), CoC_locator::integer(), Prefix::binary(), Chunk::binary(),
                    CSum::binary(), ChunkExtra::non_neg_integer()) ->
                           {ok, Filename::string(), Offset::machi_dt:file_offset()} |
                           {error, machi_client_error_reason()}.
-append_chunk(PidSpec, PlacementKey, Prefix, Chunk, CSum, ChunkExtra) ->
-    append_chunk(PidSpec, PlacementKey, Prefix, Chunk, CSum, ChunkExtra, ?DEFAULT_TIMEOUT).
+append_chunk(PidSpec, CoC_namespace, CoC_locator, Prefix, Chunk, CSum, ChunkExtra) ->
+    append_chunk(PidSpec, CoC_namespace, CoC_locator, Prefix, Chunk, CSum, ChunkExtra, ?DEFAULT_TIMEOUT).
 
--spec append_chunk(pid(), PlacementKey::binary(), Prefix::binary(),
+-spec append_chunk(pid(), CoC_namespace::binary(), CoC_locator::integer(), Prefix::binary(),
                    Chunk::binary(), CSum::binary(),
                    ChunkExtra::non_neg_integer(),
                    Timeout::non_neg_integer()) ->
                           {ok, Filename::string(), Offset::machi_dt:file_offset()} |
                           {error, machi_client_error_reason()}.
-append_chunk(PidSpec, PlacementKey, Prefix, Chunk, CSum, ChunkExtra, Timeout) ->
-    send_sync(PidSpec, {append_chunk, PlacementKey, Prefix, Chunk, CSum, ChunkExtra}, Timeout).
+append_chunk(PidSpec, CoC_namespace, CoC_locator, Prefix, Chunk, CSum, ChunkExtra, Timeout) ->
+    send_sync(PidSpec, {append_chunk, CoC_namespace, CoC_locator, Prefix, Chunk, CSum, ChunkExtra}, Timeout).
 
 -spec write_chunk(pid(), File::string(), machi_dt:file_offset(),
                   Chunk::binary(), CSum::binary()) ->
@@ -281,15 +281,14 @@ do_send_sync2({auth, User, Pass}, #state{sock=Sock}=S) ->
             Res = {bummer, {X, Y, erlang:get_stacktrace()}},
             {Res, S}
     end;
-do_send_sync2({append_chunk, PlacementKey, Prefix, Chunk, CSum, ChunkExtra},
+do_send_sync2({append_chunk, CoC_namespace, CoC_locator,
+               Prefix, Chunk, CSum, ChunkExtra},
              #state{sock=Sock, sock_id=Index, count=Count}=S) ->
     try
         ReqID = <<Index:64/big, Count:64/big>>,
-        PK = if PlacementKey == <<>> -> undefined;
-                true                 -> PlacementKey
-             end,
         CSumT = convert_csum_req(CSum, Chunk),
-        Req = #mpb_appendchunkreq{placement_key=PK,
+        Req = #mpb_appendchunkreq{coc_namespace=CoC_namespace,
+                                  coc_locator=CoC_locator,
                                   prefix=Prefix,
                                   chunk=Chunk,
                                   csum=CSumT,
diff --git a/test/machi_pb_high_client_test.erl b/test/machi_pb_high_client_test.erl
index 361eb55..9cba8bc 100644
--- a/test/machi_pb_high_client_test.erl
+++ b/test/machi_pb_high_client_test.erl
@@ -61,16 +61,17 @@ smoke_test2() ->
             %% a separate test module?  Or separate test func?
             {error, _} = ?C:auth(Clnt, "foo", "bar"),
 
-            PK = <<>>,
+            CoC_n = <<>>,            % CoC_namespace (not implemented)
+            CoC_l = 0,               % CoC_locator (not implemented)
             Prefix = <<"prefix">>,
             Chunk1 = <<"Hello, chunk!">>,
             {ok, {Off1, Size1, File1}} =
-                ?C:append_chunk(Clnt, PK, Prefix, Chunk1, none, 0),
+                ?C:append_chunk(Clnt, CoC_n, CoC_l, Prefix, Chunk1, none, 0),
             true = is_binary(File1),
             Chunk2 = "It's another chunk",
             CSum2 = {client_sha, machi_util:checksum_chunk(Chunk2)},
             {ok, {Off2, Size2, File2}} =
-                ?C:append_chunk(Clnt, PK, Prefix, Chunk2, CSum2, 1024),
+                ?C:append_chunk(Clnt, CoC_n, CoC_l, Prefix, Chunk2, CSum2, 1024),
             Chunk3 = ["This is a ", <<"test,">>, 32, [["Hello, world!"]]],
             File3 = File2,
             Off3 = Off2 + iolist_size(Chunk2),
@@ -114,7 +115,8 @@ smoke_test2() ->
             LargeBytes = binary:copy(<<"x">>, 1024*1024),
             LBCsum = {client_sha, machi_util:checksum_chunk(LargeBytes)},
             {ok, {Offx, Sizex, Filex}} =
-                ?C:append_chunk(Clnt, PK, Prefix, LargeBytes, LBCsum, 0),
+                ?C:append_chunk(Clnt, CoC_n, CoC_l,
+                                Prefix, LargeBytes, LBCsum, 0),
             ok = ?C:trim_chunk(Clnt, Filex, Offx, Sizex),
 
             %% Make sure everything was trimmed