diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 16e660245..5ba794228 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -1181,7 +1181,7 @@ ngx_http_upstream_connect(ngx_http_request_t *r, ngx_http_upstream_t *u)
         return;
     }
 
-    /* rc == NGX_OK || rc == NGX_AGAIN */
+    /* rc == NGX_OK || rc == NGX_AGAIN || rc == NGX_DONE */
 
     c = u->peer.connection;