diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 75f463ba7..6d0f4ee52 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3533,7 +3533,7 @@ ngx_http_upstream_process_non_buffered_request(ngx_http_request_t *r,
 
         if (do_write) {
 
-            if (u->out_bufs || u->busy_bufs) {
+            if (u->out_bufs || u->busy_bufs || downstream->buffered) {
                 rc = ngx_http_output_filter(r, u->out_bufs);
 
                 if (rc == NGX_ERROR) {