diff --git a/dfr.c b/dfr.c
index 2853fe4..abb4710 100644
--- a/dfr.c
+++ b/dfr.c
@@ -1248,7 +1248,7 @@ defrag_check_defrag_required(
 		frag_ratio = ((amap->n_au - amap->n_clean_au) * 100) / amap->n_full_au;
 	else
 		frag_ratio = ((amap->n_au - amap->n_clean_au) * 100) /
-					(fsi->used_clusters * CLUS_PER_AU(sb));
+					(fsi->used_clusters / CLUS_PER_AU(sb) + 1);
 
 	/*
 	 * Wake-up defrag_daemon: