diff --git a/src/joliet.c b/src/joliet.c
index 64d1119..cd54104 100644
--- a/src/joliet.c
+++ b/src/joliet.c
@@ -339,6 +339,14 @@ size_t calc_dir_size(Ecma119Image *t, JolietNode *dir)
             len += dirent_len;
         }
     }
+    
+    /*
+     * The size of a dir is always a multiple of block size, as we must add 
+     * the size of the unused space after the last directory record 
+     * (ECMA-119, 6.8.1.3)
+     */
+    len = div_up(len, BLOCK_SIZE) * BLOCK_SIZE;
+
     /* cache the len */
     dir->info.dir.len = len;
     return len;