diff --git a/test/built-ins/Temporal/Now/zonedDateTimeISO/timezone-string-datetime.js b/test/built-ins/Temporal/Now/zonedDateTimeISO/timezone-string-datetime.js
index 186d3d77a9..6247a77756 100644
--- a/test/built-ins/Temporal/Now/zonedDateTimeISO/timezone-string-datetime.js
+++ b/test/built-ins/Temporal/Now/zonedDateTimeISO/timezone-string-datetime.js
@@ -23,8 +23,20 @@ assert.sameValue(result3.timeZone.id, "-07:00", "date-time + offset is the offse
 const result4 = Temporal.Now.zonedDateTimeISO({ timeZone });
 assert.sameValue(result4.timeZone.id, "-07:00", "date-time + offset is the offset time zone (string in property bag)");
 
-timeZone = "2021-08-19T17:30-0700";
+timeZone = "2021-08-19T17:30[UTC]";
 const result5 = Temporal.Now.zonedDateTimeISO(timeZone);
-assert.sameValue(result5.timeZone.id, "-07:00", "date-time + offset is the offset time zone");
+assert.sameValue(result5.timeZone.id, "UTC", "date-time + IANA annotation is the IANA time zone");
 const result6 = Temporal.Now.zonedDateTimeISO({ timeZone });
-assert.sameValue(result6.timeZone.id, "-07:00", "date-time + offset is the offset time zone (string in property bag)");
+assert.sameValue(result6.timeZone.id, "UTC", "date-time + IANA annotation is the IANA time zone (string in property bag)");
+
+timeZone = "2021-08-19T17:30Z[UTC]";
+const result7 = Temporal.Now.zonedDateTimeISO(timeZone);
+assert.sameValue(result7.timeZone.id, "UTC", "date-time + Z + IANA annotation is the IANA time zone");
+const result8 = Temporal.Now.zonedDateTimeISO({ timeZone });
+assert.sameValue(result8.timeZone.id, "UTC", "date-time + Z + IANA annotation is the IANA time zone (string in property bag)");
+
+timeZone = "2021-08-19T17:30-07:00[UTC]";
+const result9 = Temporal.Now.zonedDateTimeISO(timeZone);
+assert.sameValue(result9.timeZone.id, "UTC", "date-time + offset + IANA annotation is the IANA time zone");
+const result10 = Temporal.Now.zonedDateTimeISO({ timeZone });
+assert.sameValue(result10.timeZone.id, "UTC", "date-time + offset + IANA annotation is the IANA time zone (string in property bag)");