diff --git a/include/starpu.h b/include/starpu.h
index 8621649be..4f52f0de9 100644
--- a/include/starpu.h
+++ b/include/starpu.h
@@ -406,7 +406,7 @@ struct starpu_conf
 	   to specify a bigger value to avoid any flushing (which
 	   would disturb the trace).
 	*/
-	unsigned trace_buffer_size;
+	uint64_t trace_buffer_size;
 	int global_sched_ctx_min_priority;
 	int global_sched_ctx_max_priority;
 
diff --git a/src/common/fxt.c b/src/common/fxt.c
index 033026d1c..9372e011b 100644
--- a/src/common/fxt.c
+++ b/src/common/fxt.c
@@ -159,7 +159,14 @@ int starpu_fxt_is_enabled()
 	return starpu_get_env_number_default("STARPU_FXT_TRACE", 1);
 }
 
-void _starpu_fxt_init_profiling(unsigned trace_buffer_size)
+void _starpu_fxt_flush_callback()
+{
+	_STARPU_MSG("FxT is flushing trace to disk !\n");
+
+	starpu_fxt_trace_user_event_string("fxt flush");
+}
+
+void _starpu_fxt_init_profiling(uint64_t trace_buffer_size)
 {
 	unsigned threadid;
 
@@ -191,7 +198,7 @@ void _starpu_fxt_init_profiling(unsigned trace_buffer_size)
 
 	threadid = _starpu_gettid();
 
-	if (fut_setup(trace_buffer_size / sizeof(unsigned long), initial_key_mask, threadid) < 0)
+	if (fut_setup(trace_buffer_size / sizeof(unsigned long), initial_key_mask, threadid, &_starpu_fxt_flush_callback) < 0)
 	{
 		perror("fut_setup");
 		STARPU_ABORT();
diff --git a/src/common/fxt.h b/src/common/fxt.h
index 808af77fa..ab2408968 100644
--- a/src/common/fxt.h
+++ b/src/common/fxt.h
@@ -313,7 +313,7 @@ static inline unsigned long _starpu_fxt_get_submit_order(void)
 long _starpu_gettid(void);
 
 /* Initialize the FxT library. */
-void _starpu_fxt_init_profiling(unsigned trace_buffer_size);
+void _starpu_fxt_init_profiling(uint64_t trace_buffer_size);
 
 /* Stop the FxT library, and generate the trace file. */
 void _starpu_stop_fxt_profiling(void);
diff --git a/src/core/workers.c b/src/core/workers.c
index 967755933..fb6cee3e3 100644
--- a/src/core/workers.c
+++ b/src/core/workers.c
@@ -1142,7 +1142,8 @@ int starpu_conf_init(struct starpu_conf *conf)
 #endif
 
 	/* 64MiB by default */
-	conf->trace_buffer_size = starpu_get_env_number_default("STARPU_TRACE_BUFFER_SIZE", 64) << 20;
+	conf->trace_buffer_size = ((uint64_t) starpu_get_env_number_default("STARPU_TRACE_BUFFER_SIZE", 64)) << 20;
+	printf("used trace_buffer_size: %lu\n", conf->trace_buffer_size);
 
 	/* Do not start performance counter collection by default */
 	conf->start_perf_counter_collection = 0;