diff --git a/src/nxt_conn_write.c b/src/nxt_conn_write.c
index 7d0a579f2..2a92f0f5d 100644
--- a/src/nxt_conn_write.c
+++ b/src/nxt_conn_write.c
@@ -118,12 +118,8 @@ nxt_conn_io_write(nxt_task_t *task, void *obj, void *data)
         }
     }
 
-    if (ret == 0 || sb.sent != 0) {
-        /*
-         * ret == 0 means a sync buffer was processed.
-         * ret == NXT_ERROR is ignored here if some data was sent,
-         * the error will be handled on the next nxt_conn_write() call.
-         */
+    if (ret == 0 || (ret != NXT_ERROR && sb.sent != 0)) {
+        /* ret == 0 means a sync buffer was processed. */
         c->sent += sb.sent;
         nxt_work_queue_add(c->write_work_queue, c->write_state->ready_handler,
                            task, c, data);
@@ -134,6 +130,21 @@ nxt_conn_io_write(nxt_task_t *task, void *obj, void *data)
         return;
     }
 
+    if (sb.sent != 0) {
+        /*
+         * Pattern D′: route to error_handler immediately when a write
+         * returns NXT_ERROR after a partial send (e.g. peer closed
+         * mid-response).  Pre-fix, this case fell through to
+         * ready_handler and the error was deferred to the next
+         * nxt_conn_io_write() call via c->socket.error.  Mirrors the
+         * TLS path's fail-fast contract; see nxt_openssl_conn_test_error.
+         */
+        c->sent += sb.sent;
+        nxt_log(task, NXT_LOG_INFO,
+                "conn write: peer closed mid-response fd:%d sent:%O",
+                c->socket.fd, sb.sent);
+    }
+
     nxt_fd_event_block_write(engine, &c->socket);
 
 error:
diff --git a/src/nxt_router.c b/src/nxt_router.c
index c994f3707..3f2161db7 100644
--- a/src/nxt_router.c
+++ b/src/nxt_router.c
@@ -5892,10 +5892,17 @@ nxt_router_get_mmap_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg)
     nxt_assert(port->type == NXT_PROCESS_APP);
 
     if (nxt_slow_path(port->app == NULL)) {
-        nxt_alert(task, "get_mmap_handler: app == NULL for reply port %PI:%d",
-                  port->pid, port->id);
+        /*
+         * Pattern D′: a NULL app pointer here is a benign race during
+         * worker shutdown / graceful reload (the app freed before its
+         * reply port was drained), not a corruption.  Demoted from
+         * ALERT so reload-under-load doesn't pollute the log.
+         */
+        nxt_log(task, NXT_LOG_INFO,
+                "get_mmap_handler: app == NULL for reply port %PI:%d "
+                "(peer likely shutting down)",
+                port->pid, port->id);
 
-        // FIXME
         nxt_port_socket_write(task, port, NXT_PORT_MSG_RPC_ERROR,
                               -1, msg->port_msg.stream, 0, NULL);