diff --git a/block/mirror.c b/block/mirror.c
index 82abc2f..0fc140a 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -87,6 +87,9 @@ static void mirror_iteration_done(MirrorOp *op)
     cluster_num = op->sector_num / s->granularity;
     nb_chunks = op->nb_sectors / s->granularity;
     bitmap_clear(s->in_flight_bitmap, cluster_num, nb_chunks);
+    if (s->cow_bitmap) {
+        bitmap_set(s->cow_bitmap, cluster_num, nb_chunks);
+    }
 
     trace_mirror_iteration_done(s, op->sector_num, op->nb_sectors);
     g_slice_free(MirrorOp, op);
@@ -217,9 +220,6 @@ static void coroutine_fn mirror_iteration(MirrorBlockJob *s)
 
         /* We have enough free space to copy these sectors.  */
         bitmap_set(s->in_flight_bitmap, next_cluster, added_chunks);
-        if (s->cow_bitmap) {
-            bitmap_set(s->cow_bitmap, next_cluster, added_chunks);
-        }
 
         nb_sectors += added_sectors;
         nb_chunks += added_chunks;