diff --git a/src/elpi_trace_elaborator.ml b/src/elpi_trace_elaborator.ml
index ca13114d..093e7593 100644
--- a/src/elpi_trace_elaborator.ml
+++ b/src/elpi_trace_elaborator.ml
@@ -664,6 +664,6 @@ let main =
 
   let cards = Trace.cards steps ~stack_frames ~aggregated_goal_success ~goal_text ~goal_attempts in
 
-  let ob = Bi_outbuf.create_channel_writer stdout in
+  let ob = Buffer.create 17 in
   write_trace ob cards;
-  Bi_outbuf.flush_channel_writer ob
+  Buffer.output_buffer stdout ob