diff --git a/src/event/ngx_event_pipe.c b/src/event/ngx_event_pipe.c
index 09b6f6a6e..bb371691b 100644
--- a/src/event/ngx_event_pipe.c
+++ b/src/event/ngx_event_pipe.c
@@ -511,6 +511,7 @@ ngx_event_pipe_write_to_downstream(ngx_event_pipe_t *p)
                 cl = p->out;
 
                 if (cl->buf->recycled
+                    && cl->buf->last_shadow
                     && bsize + cl->buf->last - cl->buf->pos > p->busy_size)
                 {
                     flush = 1;
@@ -525,6 +526,7 @@ ngx_event_pipe_write_to_downstream(ngx_event_pipe_t *p)
                 cl = p->in;
 
                 if (cl->buf->recycled
+                    && cl->buf->last_shadow
                     && bsize + cl->buf->last - cl->buf->pos > p->busy_size)
                 {
                     flush = 1;