diff --git a/block/mirror.c b/block/mirror.c
index 3b6f0c5..153758c 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1041,6 +1041,10 @@
 
 static int coroutine_fn bdrv_mirror_top_flush(BlockDriverState *bs)
 {
+    if (bs->backing == NULL) {
+        /* we can be here after failed bdrv_append in mirror_start_job */
+        return 0;
+    }
     return bdrv_co_flush(bs->backing->bs);
 }