diff --git a/glib/gdatetime.c b/glib/gdatetime.c
index 3be4eba3d..1382d3f93 100644
--- a/glib/gdatetime.c
+++ b/glib/gdatetime.c
@@ -1429,9 +1429,13 @@ parse_iso8601_time (const gchar *text, gsize length,
  *
  * Creates a #GDateTime corresponding to the given
  * [ISO 8601 formatted string](https://en.wikipedia.org/wiki/ISO_8601)
- * @text. ISO 8601 strings of the form <date><sep><time><tz> are supported.
+ * @text. ISO 8601 strings of the form <date><sep><time><tz> are supported, with
+ * some extensions from [RFC 3339](https://tools.ietf.org/html/rfc3339) as
+ * mentioned below.
  *
- * <sep> is the separator and can be either 'T', 't' or ' '.
+ * <sep> is the separator and can be either 'T', 't' or ' '. The latter two
+ * separators are an extension from
+ * [RFC 3339](https://tools.ietf.org/html/rfc3339#section-5.6).
  *
  * <date> is in the form:
  *