diff --git a/src/plugins/server/jbuffer.ml b/src/plugins/server/jbuffer.ml
index 70e5d66af55ac68ad3b4d464a644f168d18f6073..d354dc8bc22d5c498edde315774d822fb376289b 100644
--- a/src/plugins/server/jbuffer.ml
+++ b/src/plugins/server/jbuffer.ml
@@ -40,7 +40,8 @@ let flush buffer () =
     buffer.rjson <- js :: buffer.rjson ;
     FCBuffer.clear t
 
-let push_tag buffer tag =
+let push_tag buffer stag =
+  let tag = Transitioning.Format.string_of_stag stag in
   flush buffer () ;
   buffer.stack <- ( tag , buffer.rjson ) :: buffer.stack ;
   buffer.rjson <- []
@@ -83,15 +84,15 @@ let create ?indent ?margin () =
       Format.pp_set_max_indent fmt (max 0 (min k (m-10)))
   end ;
   begin
-    let open Format in
-    pp_set_formatter_tag_functions fmt {
-      print_open_tag = no_mark ;
-      print_close_tag = no_mark ;
-      mark_open_tag = mark_open_tag buffer ;
-      mark_close_tag = mark_close_tag buffer ;
+    let open Transitioning.Format in
+    pp_set_formatter_stag_functions fmt {
+      print_open_stag = no_mark ;
+      print_close_stag = no_mark ;
+      mark_open_stag = mark_open_tag buffer ;
+      mark_close_stag = mark_close_tag buffer ;
     } ;
-    pp_set_print_tags fmt false ;
-    pp_set_mark_tags fmt true ;
+    Format.pp_set_print_tags fmt false ;
+    Format.pp_set_mark_tags fmt true ;
   end ;
   buffer
 
diff --git a/src/plugins/server/jbuffer.mli b/src/plugins/server/jbuffer.mli
index 3e1e02a1beae8615cf925e52b980b093749766c1..70d9062f0e5d69d7585289234f4de97f0625049c 100644
--- a/src/plugins/server/jbuffer.mli
+++ b/src/plugins/server/jbuffer.mli
@@ -46,8 +46,8 @@ val bprintf : buffer -> ('a,Format.formatter,unit) format -> 'a
 
 val append : buffer -> string -> int -> int -> unit
 val flush : buffer -> unit -> unit
-val push_tag : buffer -> Format.tag -> unit
-val pop_tag : buffer -> Format.tag -> unit
+val push_tag : buffer -> Transitioning.Format.stag -> unit
+val pop_tag : buffer -> Transitioning.Format.stag -> unit
 
 (** Flushes the buffer and returns its JSON enoding. This pops all pending
     tags. *)