diff --git a/monitor.c b/monitor.c
index 129badcd1a..a3ec65f1d9 100644
--- a/monitor.c
+++ b/monitor.c
@@ -283,6 +283,7 @@ static void monitor_protocol_emitter(Monitor *mon, QObject *data)
     if (!monitor_has_error(mon)) {
         /* success response */
         if (data) {
+            assert(qobject_type(data) == QTYPE_QDICT);
             qobject_incref(data);
             qdict_put_obj(qmp, "return", data);
         } else {