diff --git a/package.json b/package.json
index 42f8531..3d03722 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "fecha",
-  "version": "4.1.0",
+  "version": "4.2.0",
   "description": "Date formatting and parsing",
   "main": "lib/fecha.umd.js",
   "module": "lib/fecha.js",
diff --git a/test.js b/test.js
index 21be749..cb9c309 100644
--- a/test.js
+++ b/test.js
@@ -529,6 +529,13 @@ testFormat(
 );
 testFormat("current date", new Date(), "YYYY", "" + new Date().getFullYear());
 testFormat("mask", new Date(1999, 0, 2), "mediumDate", "Jan 2, 1999");
+testFormat("mask isoDate", new Date(1999, 0, 2), "isoDate", "1999-01-02");
+testFormat(
+  "mask isoDateTime",
+  new Date(1999, 0, 2, 5, 7, 9),
+  "isoDateTime",
+  "1999-01-02T05:07:09-05:00"
+);
 testFormat(
   "number date",
   1325376000000,