diff --git a/event.c b/event.c
index 5586cd3..7a7c165 100644
--- a/event.c
+++ b/event.c
@@ -413,6 +413,8 @@ int event_base_once (struct event_base *base, int fd, short events, void (*cb)(i
 
   ev_once (EV_A_ fd, events & (EV_READ | EV_WRITE), ev_tv_get (tv), ev_x_once_cb, (void *)once);
 
+  free (once);
+
   return 0;
 }