diff --git a/apps/emqx_ft/src/emqx_ft.erl b/apps/emqx_ft/src/emqx_ft.erl
index 6a6599366..baa0126d6 100644
--- a/apps/emqx_ft/src/emqx_ft.erl
+++ b/apps/emqx_ft/src/emqx_ft.erl
@@ -143,26 +143,37 @@ on_message_puback(PacketId, #message{topic = Topic} = Msg, _PubRes, _RC) ->
 %% TODO Move to emqx_ft_mqtt?
 
 on_file_command(PacketId, Msg, FileCommand) ->
-    case string:split(FileCommand, <<"/">>, all) of
-        [FileId, <<"init">>] ->
-            on_init(PacketId, Msg, transfer(Msg, FileId));
-        [FileId, <<"fin">>, FinalSizeBin | MaybeChecksum] when length(MaybeChecksum) =< 1 ->
+    case emqx_topic:tokens(FileCommand) of
+        [FileIdIn | Rest] ->
+            validate([{fileid, FileIdIn}], fun([FileId]) ->
+                on_file_command(PacketId, FileId, Msg, Rest)
+            end);
+        [] ->
+            ?RC_UNSPECIFIED_ERROR
+    end.
+
+on_file_command(PacketId, FileId, Msg, FileCommand) ->
+    Transfer = transfer(Msg, FileId),
+    case FileCommand of
+        [<<"init">>] ->
+            on_init(PacketId, Msg, Transfer);
+        [<<"fin">>, FinalSizeBin | MaybeChecksum] when length(MaybeChecksum) =< 1 ->
             ChecksumBin = emqx_maybe:from_list(MaybeChecksum),
             validate(
                 [{size, FinalSizeBin}, {{maybe, checksum}, ChecksumBin}],
                 fun([FinalSize, Checksum]) ->
-                    on_fin(PacketId, Msg, transfer(Msg, FileId), FinalSize, Checksum)
+                    on_fin(PacketId, Msg, Transfer, FinalSize, Checksum)
                 end
             );
-        [FileId, <<"abort">>] ->
-            on_abort(Msg, transfer(Msg, FileId));
-        [FileId, OffsetBin] ->
+        [<<"abort">>] ->
+            on_abort(Msg, Transfer);
+        [OffsetBin] ->
             validate([{offset, OffsetBin}], fun([Offset]) ->
-                on_segment(PacketId, Msg, transfer(Msg, FileId), Offset, undefined)
+                on_segment(PacketId, Msg, Transfer, Offset, undefined)
             end);
-        [FileId, OffsetBin, ChecksumBin] ->
+        [OffsetBin, ChecksumBin] ->
             validate([{offset, OffsetBin}, {checksum, ChecksumBin}], fun([Offset, Checksum]) ->
-                on_segment(PacketId, Msg, transfer(Msg, FileId), Offset, Checksum)
+                on_segment(PacketId, Msg, Transfer, Offset, Checksum)
             end);
         _ ->
             ?RC_UNSPECIFIED_ERROR
@@ -358,6 +369,13 @@ validate(Validations, Fun) ->
 
 do_validate([], Parsed) ->
     {ok, lists:reverse(Parsed)};
+do_validate([{fileid, FileId} | Rest], Parsed) ->
+    case byte_size(FileId) of
+        S when S > 0 ->
+            do_validate(Rest, [FileId | Parsed]);
+        0 ->
+            {error, {invalid_fileid, FileId}}
+    end;
 do_validate([{offset, Offset} | Rest], Parsed) ->
     case string:to_integer(Offset) of
         {Int, <<>>} ->
diff --git a/apps/emqx_ft/src/emqx_ft_storage_fs.erl b/apps/emqx_ft/src/emqx_ft_storage_fs.erl
index d3331a091..667ca091a 100644
--- a/apps/emqx_ft/src/emqx_ft_storage_fs.erl
+++ b/apps/emqx_ft/src/emqx_ft_storage_fs.erl
@@ -93,7 +93,6 @@
     % Quota? Some lower level errors?
     ok | {error, conflict} | {error, file_error()}.
 store_filemeta(Storage, Transfer, Meta) ->
-    % TODO safeguard against bad clientids / fileids.
     Filepath = mk_filepath(Storage, Transfer, [?FRAGDIR], ?MANIFEST),
     case read_file(Filepath, fun decode_filemeta/1) of
         {ok, Meta} ->
diff --git a/apps/emqx_ft/test/emqx_ft_SUITE.erl b/apps/emqx_ft/test/emqx_ft_SUITE.erl
index be3b19a8c..37cc38d4f 100644
--- a/apps/emqx_ft/test/emqx_ft_SUITE.erl
+++ b/apps/emqx_ft/test/emqx_ft_SUITE.erl
@@ -159,6 +159,13 @@ t_invalid_topic_format(Config) ->
         emqtt:publish(C, <<"$file">>, <<>>, 1)
     ).
 
+t_invalid_fileid(Config) ->
+    C = ?config(client, Config),
+    ?assertRCName(
+        unspecified_error,
+        emqtt:publish(C, <<"$file//init">>, <<>>, 1)
+    ).
+
 t_simple_transfer(Config) ->
     C = ?config(client, Config),