diff --git a/README.md b/README.md
index 0a019c40a..9c5b1d97d 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,7 @@ Validator | Description
**isISSN(str [, options])** | check if the string is an [ISSN](https://en.wikipedia.org/wiki/International_Standard_Serial_Number).
`options` is an object which defaults to `{ case_sensitive: false, require_hyphen: false }`. If `case_sensitive` is true, ISSNs with a lowercase `'x'` as the check digit are rejected.
**isISIN(str)** | check if the string is an [ISIN][ISIN] (stock/security identifier).
**isISO8601(str)** | check if the string is a valid [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) date.
+**isRFC3339(str)** | check if the string is a valid [RFC 3339](https://tools.ietf.org/html/rfc3339) date.
**isISO31661Alpha2(str)** | check if the string is a valid [ISO 3166-1 alpha-2](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) officially assigned country code.
**isISRC(str)** | check if the string is a [ISRC](https://en.wikipedia.org/wiki/International_Standard_Recording_Code).
**isIn(str, values)** | check if the string is in a array of allowed values.