diff --git a/kernel/fatfs.c b/kernel/fatfs.c
index 411e2d26..ec89418f 100644
--- a/kernel/fatfs.c
+++ b/kernel/fatfs.c
@@ -1028,6 +1028,12 @@ COUNT map_cluster(REG f_node_ptr fnp, COUNT mode)
 
     fnp->f_cluster = cluster;
     fnp->f_cluster_offset++;
+    fnp->f_dir.dir_size =
+      ((ULONG)fnp->f_cluster
+      * (ULONG)fnp->f_dpb->dpb_secsize)
+      <<
+      fnp->f_dpb->dpb_shftcnt;
+    merge_file_changes(fnp, FALSE);
   }
 
 #ifdef DISPLAY_GETBLOCK