diff --git a/block/nbd.c b/block/nbd.c
index 5f18f78a94..d085554f21 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -866,6 +866,7 @@ typedef struct NBDReplyChunkIter {
 static void nbd_iter_channel_error(NBDReplyChunkIter *iter,
                                    int ret, Error **local_err)
 {
+    assert(local_err && *local_err);
     assert(ret < 0);
 
     if (!iter->ret) {