diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index f7ac4a4ebd..4a4af73218 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2500,7 +2500,6 @@ ngx_http_upstream_send_response(ngx_http_request_t *r, ngx_http_upstream_t *u)
 
         } else {
             u->cacheable = 0;
-            r->headers_out.last_modified_time = -1;
         }
     }