diff --git a/src/event/event_linux.c b/src/event/event_linux.c
index a829dead..df9e98f8 100644
--- a/src/event/event_linux.c
+++ b/src/event/event_linux.c
@@ -213,6 +213,9 @@ neu_event_timer_t *neu_event_add_timer(neu_events_t *          events,
         .it_interval.tv_nsec = timer.millisecond * 1000 * 1000,
     };
     int index = get_free_event(events);
+    if (index < 0) {
+        zlog_notice(neuron, "no free event: %d", events->epoll_fd);
+    }
     assert(index >= 0);
 
     neu_event_timer_t *timer_ctx = &events->event_datas[index].ctx.timer;