diff --git a/packages/date/README.md b/packages/date/README.md
index 8edd4e94a8538f..ed2dfdd4790324 100644
--- a/packages/date/README.md
+++ b/packages/date/README.md
@@ -50,7 +50,7 @@ _Parameters_
 
 -   _dateFormat_ `string`: PHP-style formatting string. See php.net/date.
 -   _dateValue_ `Moment | Date | string | undefined`: Date object or string, parsable by moment.js.
--   _timezone_ `string | number | boolean | undefined`: Timezone to output result in or a UTC offset. Defaults to timezone from site. Notice: `boolean` is effectively deprecated, but still supported for backward compatibility reasons.
+-   _timezone_ `string | number | boolean | undefined=`: Timezone to output result in or a UTC offset. Defaults to timezone from site. Notice: `boolean` is effectively deprecated, but still supported for backward compatibility reasons.
 
 _Returns_
 
diff --git a/packages/date/src/index.js b/packages/date/src/index.js
index 811ae8d009a048..b632de3a7431f6 100644
--- a/packages/date/src/index.js
+++ b/packages/date/src/index.js
@@ -525,26 +525,22 @@ export function gmdate( dateFormat, dateValue = new Date() ) {
  * Backward Compatibility Notice: if `timezone` is set to `true`, the function
  * behaves like `gmdateI18n`.
  *
- * @param {string}                                dateFormat PHP-style formatting string.
- *                                                           See php.net/date.
- * @param {Moment | Date | string | undefined}    dateValue  Date object or string, parsable by
- *                                                           moment.js.
- * @param {string | number | boolean | undefined} timezone   Timezone to output result in or a
- *                                                           UTC offset. Defaults to timezone from
- *                                                           site. Notice: `boolean` is effectively
- *                                                           deprecated, but still supported for
- *                                                           backward compatibility reasons.
+ * @param {string}                                 dateFormat PHP-style formatting string.
+ *                                                            See php.net/date.
+ * @param {Moment | Date | string | undefined}     dateValue  Date object or string, parsable by
+ *                                                            moment.js.
+ * @param {string | number | boolean | undefined=} timezone   Timezone to output result in or a
+ *                                                            UTC offset. Defaults to timezone from
+ *                                                            site. Notice: `boolean` is effectively
+ *                                                            deprecated, but still supported for
+ *                                                            backward compatibility reasons.
  *
  * @see https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
  * @see https://en.wikipedia.org/wiki/ISO_8601#Time_offsets_from_UTC
  *
  * @return {string} Formatted date.
  */
-export function dateI18n(
-	dateFormat,
-	dateValue = new Date(),
-	timezone = undefined
-) {
+export function dateI18n( dateFormat, dateValue = new Date(), timezone ) {
 	if ( true === timezone ) {
 		return gmdateI18n( dateFormat, dateValue );
 	}