diff --git a/src/shadow-image.c b/src/shadow-image.c
index a09a63d..36a37ad 100644
--- a/src/shadow-image.c
+++ b/src/shadow-image.c
@@ -498,7 +498,7 @@ static enum ec3_status copy_cached_cluster(
 	cluster.c_len = encoded_size;
 
 	image->img_nr_clusters++;
-	image->img_nr_bytes += nr_read;
+	image->img_nr_bytes += nr_written;
 
 	cluster_table_put(&image->img_cluster_table, &cluster);