diff --git a/polyfill/test/Duration/constructor/compare/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/Duration/constructor/compare/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..586bc1bff6
--- /dev/null
+++ b/polyfill/test/Duration/constructor/compare/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,36 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.compare
+info: |
+    sec-temporal.duration.compare steps 4–6:
+      4. Let _relativeTo_ be ? ToRelativeTemporalObject(_options_).
+      5. Let _shift1_ be ! CalculateOffsetShift(_relativeTo_, _one_.[[Years]], [...], _one_.[[Nanoseconds]]).
+      6. Let _shift2_ be ! CalculateOffsetShift(_relativeTo_, _two_.[[Years]], [...], _two_.[[Nanoseconds]]).
+    sec-temporal-torelativetemporalobject step 6.d:
+      d. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNs_, _timeZone_, *"compatible"*, *"reject"*).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-calculateoffsetshift step 4:
+      4. Let _after_ be ? AddZonedDateTime(_relativeTo_.[[Nanoseconds]], _relativeTo_.[[TimeZone]], _relativeTo_.[[Calendar]], _y_, [...], _ns_).
+    sec-temporal-addzoneddatetime step 8:
+      8. Let _intermediateInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _intermediateDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2000-01-01T00:00:00", // called once on the input relativeTo object
+  "2001-01-01T00:00:00", // called once on relativeTo plus the first operand
+  "2001-02-01T00:00:00", // called once on relativeTo plus the second operand
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const duration1 = new Temporal.Duration(1);
+  const duration2 = new Temporal.Duration(0, 13);
+  Temporal.Duration.compare(duration1, duration2, { relativeTo: { year: 2000, month: 1, day: 1, timeZone } });
+}, expected);
diff --git a/polyfill/test/Duration/prototype/add/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/Duration/prototype/add/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..6aee2688e9
--- /dev/null
+++ b/polyfill/test/Duration/prototype/add/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,41 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.add
+info: |
+    sec-temporal.duration.prototype.add steps 5–6:
+      5. Let _relativeTo_ be ? ToRelativeTemporalObject(_options_).
+      6. Let _result_ be ? AddDuration(_duration_.[[Years]], [...], _duration_.[[Nanoseconds]], _other_.[[Years]], [...], _other_.[[Nanoseconds]], _relativeTo_).
+    sec-temporal-torelativetemporalobject step 6.d:
+      d. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNs_, _timeZone_, *"compatible"*, *"reject"*).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-addduration steps 7.d–e and 7.g.i:
+      d. Let _intermediateNs_ be ? AddZonedDateTime(_relativeTo_.[[Nanoseconds]], _timeZone_, _calendar_, _y1_, [...], _ns1_).
+      e. Let _endNs_ be ? AddZonedDateTime(_intermediateNs_, _timeZone_, _calendar_, _y2_, [...], _ns2_).
+      [...]
+        i. Let _result_ be ? DifferenceZonedDateTime(_relativeTo_.[[Nanoseconds]], _endNs_, _timeZone_, _calendar_, _largestUnit_).
+    sec-temporal-differencezoneddatetime step 8:
+      8. Let _intermediateNs_ be ? AddZonedDateTime(_ns1_, _timeZone_, _calendar_, _dateDifference_.[[Years]], _dateDifference_.[[Months]], _dateDifference_.[[Weeks]], 0, 0, 0, 0, 0, 0, 0).
+    sec-temporal-addzoneddatetime step 8:
+      8. Let _intermediateInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _intermediateDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2000-01-01T09:00:00", // called once on the input relativeTo object
+  "2001-01-01T09:00:00", // called once on relativeTo plus the receiver
+  "2002-01-01T09:00:00", // called once on relativeTo plus the receiver plus the argument
+  "2002-01-01T09:00:00", // called once on relativeTo plus the years, months, and weeks from the difference of relativeTo minus endNs
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const duration1 = new Temporal.Duration(1);
+  const duration2 = new Temporal.Duration(0, 12);
+  duration1.add(duration2, { relativeTo: { year: 2000, month: 1, day: 1, hour: 9, timeZone } });
+}, expected);
diff --git a/polyfill/test/Duration/prototype/round/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/Duration/prototype/round/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..dacdc9e97b
--- /dev/null
+++ b/polyfill/test/Duration/prototype/round/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,43 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.round
+info: |
+    sec-temporal.duration.prototype.round steps 19, 21, and 24:
+      19. Let _relativeTo_ be ? ToRelativeTemporalObject(_options_).
+      21. Let _roundResult_ be ? RoundDuration(_unbalanceResult_.[[Years]], [...], _unbalanceResult_.[[Days]], _duration_.[[Hours]], [...], _duration_.[[Nanoseconds]], _roundingIncrement_, _smallestUnit_, _roundingMode_, _relativeTo_).
+      24. If _relativeTo_ has an [[InitializedTemporalZonedDateTime]] internal slot, then
+        a. Set _relativeTo_ to ? MoveRelativeZonedDateTime(_relativeTo_, _balanceResult_.[[Years]], _balanceResult_.[[Months]], _balanceResult_.[[Weeks]], 0).
+    sec-temporal-torelativetemporalobject step 6.d:
+      d. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNs_, _timeZone_, *"compatible"*, *"reject"*).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-roundduration step 5.c–d:
+      c. If _zonedRelativeTo_ is not *undefined*, then
+        i. Let _intermediate_ be ? MoveRelativeZonedDateTime(_zonedRelativeTo_, _years_, _months_, _weeks_, _days_).
+      d. Let _result_ be ? NanosecondsToDays(_nanoseconds_, _intermediate_).
+    sec-temporal-moverelativezoneddatetime step 1:
+      1. Let _intermediateNs_ be ? AddZonedDateTime(_zonedDateTime_.[[Nanoseconds]], _zonedDateTime_.[[TimeZone]], _zonedDateTime_.[[Calendar]], _years_, _months_, _weeks_, _days_, 0, 0, 0, 0, 0, 0).
+    sec-temporal-nanosecondstodays step 13:
+      13. Let _intermediateNs_ be ? AddZonedDateTime(_startNs_, _relativeTo_.[[TimeZone]], _relativeTo_.[[Calendar]], 0, 0, 0, _days_, 0, 0, 0, 0, 0, 0).
+    sec-temporal-addzoneddatetime step 8:
+      8. Let _intermediateInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _intermediateDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2000-01-01T00:00:00", // called once on the input relativeTo object
+  "2001-02-09T00:00:00", // called once on relativeTo plus years, months, weeks, days from the receiver
+  "2001-02-10T00:00:00", // called once on the previous value plus the calendar days difference between that and the time part of the duration
+  "2001-02-01T00:00:00", // called once on relativeTo plus the years, months, and weeks part of the balance result
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const duration = new Temporal.Duration(1, 1, 1, 1, 1, 1, 1);
+  duration.round({ smallestUnit: 'months', relativeTo: { year: 2000, month: 1, day: 1, timeZone } });
+}, expected);
diff --git a/polyfill/test/Duration/prototype/subtract/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/Duration/prototype/subtract/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..d0112ed9d2
--- /dev/null
+++ b/polyfill/test/Duration/prototype/subtract/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,41 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.subtract
+info: |
+    sec-temporal.duration.prototype.subtract steps 5–6:
+      5. Let _relativeTo_ be ? ToRelativeTemporalObject(_options_).
+      6. Let _result_ be ? AddDuration(_duration_.[[Years]], [...], _duration_.[[Nanoseconds]], −_other_.[[Years]], [...], −_other_.[[Nanoseconds]], _relativeTo_).
+    sec-temporal-torelativetemporalobject step 6.d:
+      d. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNs_, _timeZone_, *"compatible"*, *"reject"*).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-addduration steps 7.d–e and 7.g.i:
+      d. Let _intermediateNs_ be ? AddZonedDateTime(_relativeTo_.[[Nanoseconds]], _timeZone_, _calendar_, _y1_, [...], _ns1_).
+      e. Let _endNs_ be ? AddZonedDateTime(_intermediateNs_, _timeZone_, _calendar_, _y2_, [...], _ns2_).
+      [...]
+        i. Let _result_ be ? DifferenceZonedDateTime(_relativeTo_.[[Nanoseconds]], _endNs_, _timeZone_, _calendar_, _largestUnit_).
+    sec-temporal-differencezoneddatetime step 8:
+      8. Let _intermediateNs_ be ? AddZonedDateTime(_ns1_, _timeZone_, _calendar_, _dateDifference_.[[Years]], _dateDifference_.[[Months]], _dateDifference_.[[Weeks]], 0, 0, 0, 0, 0, 0, 0).
+    sec-temporal-addzoneddatetime step 8:
+      8. Let _intermediateInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _intermediateDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2000-01-01T09:00:00", // called once on the input relativeTo object
+  "2001-01-01T09:00:00", // called once on relativeTo plus the receiver
+  "1999-12-01T09:00:00", // called once on relativeTo plus the receiver minus the argument
+  "1999-12-01T09:00:00", // called once on relativeTo plus the years, months, and weeks from the difference of relativeTo minus endNs
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const duration1 = new Temporal.Duration(1);
+  const duration2 = new Temporal.Duration(0, 13);
+  duration1.subtract(duration2, { relativeTo: { year: 2000, month: 1, day: 1, hour: 9, timeZone } });
+}, expected);
diff --git a/polyfill/test/Duration/prototype/total/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/Duration/prototype/total/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..0308cd7665
--- /dev/null
+++ b/polyfill/test/Duration/prototype/total/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,31 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.duration.prototype.total
+info: |
+    sec-temporal.duration.prototype.total steps 4 and 10:
+      4. Let _relativeTo_ be ? ToRelativeTemporalObject(_options_).
+      10. Let _balanceResult_ be ? BalanceDuration(_unbalanceResult_.[[Days]], [...], _unbalanceResult_.[[Nanoseconds]], _unit_, _intermediate_).
+    sec-temporal-torelativetemporalobject step 6.d:
+      d. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNs_, _timeZone_, *"compatible"*, *"reject"*).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-addzoneddatetime step 8:
+      8. Let _intermediateInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _intermediateDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2000-01-01T00:00:00", // called once on the input relativeTo if ZonedDateTime
+  "2001-02-09T00:00:00", // called once on the intermediate ZonedDateTime with the calendar parts of the Duration added
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const duration = new Temporal.Duration(1, 1, 1, 1, 1, 1, 1);
+  duration.total({ unit: 'seconds', relativeTo: { year: 2000, month: 1, day: 1, timeZone } });
+}, expected);
diff --git a/polyfill/test/PlainDate/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/PlainDate/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..e74609ee70
--- /dev/null
+++ b/polyfill/test/PlainDate/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,40 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindate.prototype.tozoneddatetime
+info: |
+    sec-temporal.plaindate.prototype.tozoneddatetime step 7:
+      7. Let _instant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _temporalDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-builtintimezonegetinstantfor step 14:
+      14. Assert: _disambiguation_ is *"compatible"* or *"later"*.
+    sec-temporal-builtintimezonegetinstantfor step 16:
+      16. Set _possibleInstants_ to ? GetPossibleInstantsFor(_timeZone_, _later_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [compareArray.js, temporalHelpers.js]
+---*/
+
+const expected1 = [
+  "2000-05-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const date = new Temporal.PlainDate(2000, 5, 2);
+  date.toZonedDateTime(timeZone);
+}, expected1);
+
+// Same, but test the other path where the time doesn't exist and
+// GetPossibleInstantsFor is called again on a later time
+
+const expected2 = [
+  "2030-01-01T00:30:00",
+  "2030-01-01T01:30:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const date = new Temporal.PlainDate(2030, 1, 1);
+  date.toZonedDateTime({ plainTime: new Temporal.PlainTime(0, 30), timeZone });
+}, expected2);
diff --git a/polyfill/test/PlainDateTime/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/PlainDateTime/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..69cc0843a6
--- /dev/null
+++ b/polyfill/test/PlainDateTime/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,40 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindatetime.prototype.tozoneddatetime
+info: |
+    sec-temporal.plaindatetime.prototype.tozoneddatetime step 6:
+      6. Let _instant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _temporalDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-builtintimezonegetinstantfor step 14:
+      14. Assert: _disambiguation_ is *"compatible"* or *"later"*.
+    sec-temporal-builtintimezonegetinstantfor step 16:
+      16. Set _possibleInstants_ to ? GetPossibleInstantsFor(_timeZone_, _later_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [compareArray.js, temporalHelpers.js]
+---*/
+
+const expected1 = [
+  "2000-05-02T12:34:56.987654321",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.PlainDateTime(2000, 5, 2, 12, 34, 56, 987, 654, 321);
+  datetime.toZonedDateTime(timeZone);
+}, expected1);
+
+// Same, but test the other path where the time doesn't exist and
+// GetPossibleInstantsFor is called again on a later time
+
+const expected2 = [
+  "2030-01-01T00:30:00",
+  "2030-01-01T01:30:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.PlainDateTime(2030, 1, 1, 0, 30);
+  datetime.toZonedDateTime(timeZone);
+}, expected2);
diff --git a/polyfill/test/PlainTime/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/PlainTime/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..88c276294a
--- /dev/null
+++ b/polyfill/test/PlainTime/prototype/toZonedDateTime/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,40 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaintime.prototype.tozoneddatetime
+info: |
+    sec-temporal.plaintime.prototype.tozoneddatetime step 10:
+      10. Let _instant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _temporalDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-builtintimezonegetinstantfor step 14:
+      14. Assert: _disambiguation_ is *"compatible"* or *"later"*.
+    sec-temporal-builtintimezonegetinstantfor step 16:
+      16. Set _possibleInstants_ to ? GetPossibleInstantsFor(_timeZone_, _later_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [compareArray.js, temporalHelpers.js]
+---*/
+
+const expected1 = [
+  "2000-05-02T12:34:56.987654321",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const time = new Temporal.PlainTime(12, 34, 56, 987, 654, 321);
+  time.toZonedDateTime({ plainDate: new Temporal.PlainDate(2000, 5, 2), timeZone });
+}, expected1);
+
+// Same, but test the other path where the time doesn't exist and
+// GetPossibleInstantsFor is called again on a later time
+
+const expected2 = [
+  "2030-01-01T00:30:00",
+  "2030-01-01T01:30:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const time = new Temporal.PlainTime(0, 30);
+  time.toZonedDateTime({ plainDate: new Temporal.PlainDate(2030, 1, 1), timeZone });
+}, expected2);
diff --git a/polyfill/test/ZonedDateTime/constructor/compare/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/constructor/compare/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..5e068c0979
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/constructor/compare/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,41 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.compare
+info: |
+    sec-temporal.zoneddatetime.compare steps 1–2:
+      1. Set _one_ to ? ToTemporalZonedDateTime(_one_).
+      2. Set _two_ to ? ToTemporalZonedDateTime(_two_).
+    sec-temporal-totemporalzoneddatetime step 7:
+      7. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, _disambiguation_, _offset_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected1 = [
+  "2000-05-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  Temporal.ZonedDateTime.compare(
+    { year: 2000, month: 5, day: 2, timeZone },
+    { year: 2001, month: 6, day: 3, timeZone: "UTC" },
+  );
+}, expected1);
+
+// Same, but on the other operand
+
+const expected2 = [
+  "2001-06-03T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  Temporal.ZonedDateTime.compare(
+    { year: 2000, month: 5, day: 2, timeZone: "UTC" },
+    { year: 2001, month: 6, day: 3, timeZone },
+  );
+}, expected2);
diff --git a/polyfill/test/ZonedDateTime/constructor/from/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/constructor/from/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..0d9376c364
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/constructor/from/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,24 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.from
+info: |
+    sec-temporal.zoneddatetime.from step 3:
+      3. Return ? ToTemporalZonedDateTime(_item_, _options_).
+    sec-temporal-totemporalzoneddatetime step 7:
+      7. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, _disambiguation_, _offset_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2000-05-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  Temporal.ZonedDateTime.from({ year: 2000, month: 5, day: 2, timeZone });
+}, expected);
diff --git a/polyfill/test/ZonedDateTime/prototype/equals/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/prototype/equals/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..460063be18
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/prototype/equals/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,36 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.equals
+info: |
+    sec-temporal.zoneddatetime.prototype.equals step 3:
+      3. Set _other_ to ? ToTemporalZonedDateTime(_other_).
+    sec-temporal-totemporalzoneddatetime step 7:
+      7. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, _disambiguation_, _offset_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+// Not called on the instance's time zone
+
+const expected1 = [];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, timeZone);
+  datetime.equals({ year: 2005, month: 6, day: 2, timeZone: "UTC" });
+}, expected1);
+
+// Called on the argument's time zone
+
+const expected2 = [
+  "2005-06-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, "UTC");
+  datetime.equals({ year: 2005, month: 6, day: 2, timeZone });
+}, expected2);
diff --git a/polyfill/test/ZonedDateTime/prototype/hoursInDay/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/prototype/hoursInDay/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..184319bef8
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/prototype/hoursInDay/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,43 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-get-temporal.zoneddatetime.prototype.hoursinday
+info: |
+    sec-get-temporal.zoneddatetime.prototype.hoursinday steps 13–14:
+      13. Let _todayInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _today_, *"compatible"*).
+      14. Let _tomorrowInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _tomorrow_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-builtintimezonegetinstantfor step 14:
+      14. Assert: _disambiguation_ is *"compatible"* or *"later"*.
+    sec-temporal-builtintimezonegetinstantfor step 16:
+      16. Set _possibleInstants_ to ? GetPossibleInstantsFor(_timeZone_, _later_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [compareArray.js, temporalHelpers.js]
+---*/
+
+const expected1 = [
+  "2001-09-09T00:00:00",
+  "2001-09-10T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, timeZone);
+  datetime.hoursInDay;
+}, expected1);
+
+// Same, but test the other path where the time doesn't exist and
+// GetPossibleInstantsFor is called again on a later time
+
+const expected2 = [
+  "2030-01-01T00:00:00",
+  "2030-01-01T01:00:00",
+  "2030-01-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_893_457_800_000_000_000n, timeZone);
+  datetime.hoursInDay;
+}, expected2);
diff --git a/polyfill/test/ZonedDateTime/prototype/round/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/prototype/round/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..cb1a64ebef
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/prototype/round/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,31 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.round
+info: |
+    sec-temporal.zoneddatetime.prototype.round steps 14, 16, and 20:
+      14. Let _instantStart_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _dtStart_, *"compatible"*).
+      16. Let _endNs_ be ? AddZonedDateTime(_startNs_, _timeZone_, _zonedDateTime_.[[Calendar]], 0, 0, 0, 1, 0, 0, 0, 0, 0, 0).
+      20. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_roundResult_.[[Year]], [...], _roundResult_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, *"compatible"*, *"prefer"*).
+    sec-temporal-addzoneddatetime step 8:
+      8. Let _intermediateInstant_ be ? BuiltinTimeZoneGetInstantFor(_timeZone_, _intermediateDateTime_, *"compatible"*).
+    sec-temporal-builtintimezonegetinstantfor step 1:
+      1. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2001-09-09T00:00:00", // called once on midnight of the input datetime
+  "2001-09-10T00:00:00", // called once on the previous value plus one calendar day
+  "2001-09-09T02:00:00",  // called once on the rounding result
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, timeZone);
+  datetime.round({ smallestUnit: 'hour' });
+}, expected);
diff --git a/polyfill/test/ZonedDateTime/prototype/since/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/prototype/since/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..7c657f3cd2
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/prototype/since/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,36 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.since
+info: |
+    sec-temporal.zoneddatetime.prototype.since step 3:
+      3. Set _other_ to ? ToTemporalZonedDateTime(_other_).
+    sec-temporal-totemporalzoneddatetime step 7:
+      7. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, _disambiguation_, _offset_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+// Not called on the instance's time zone
+
+const expected1 = [];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, timeZone);
+  datetime.since({ year: 2005, month: 6, day: 2, timeZone: "UTC" });
+}, expected1);
+
+// Called on the argument's time zone
+
+const expected2 = [
+  "2005-06-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, "UTC");
+  datetime.since({ year: 2005, month: 6, day: 2, timeZone });
+}, expected2);
diff --git a/polyfill/test/ZonedDateTime/prototype/until/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/prototype/until/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..b38d65e10d
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/prototype/until/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,36 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.until
+info: |
+    sec-temporal.zoneddatetime.prototype.until step 3:
+      3. Set _other_ to ? ToTemporalZonedDateTime(_other_).
+    sec-temporal-totemporalzoneddatetime step 7:
+      7. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_result_.[[Year]], [...], _result_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, _disambiguation_, _offset_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+// Not called on the instance's time zone
+
+const expected1 = [];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, timeZone);
+  datetime.until({ year: 2005, month: 6, day: 2, timeZone: "UTC" });
+}, expected1);
+
+// Called on the argument's time zone
+
+const expected2 = [
+  "2005-06-02T00:00:00",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, "UTC");
+  datetime.until({ year: 2005, month: 6, day: 2, timeZone });
+}, expected2);
diff --git a/polyfill/test/ZonedDateTime/prototype/with/timezone-getpossibleinstantsfor-iterable.js b/polyfill/test/ZonedDateTime/prototype/with/timezone-getpossibleinstantsfor-iterable.js
new file mode 100644
index 0000000000..8a169ec71b
--- /dev/null
+++ b/polyfill/test/ZonedDateTime/prototype/with/timezone-getpossibleinstantsfor-iterable.js
@@ -0,0 +1,23 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.with
+info: |
+    sec-temporal.zoneddatetime.prototype.with step 24:
+      24. Let _epochNanoseconds_ be ? InterpretISODateTimeOffset(_dateTimeResult_.[[Year]], [...], _dateTimeResult_.[[Nanosecond]], _offsetNanoseconds_, _timeZone_, _disambiguation_, _offset_).
+    sec-temporal-interpretisodatetimeoffset step 7:
+      7. Let _possibleInstants_ be ? GetPossibleInstantsFor(_timeZone_, _dateTime_).
+    sec-temporal-getpossibleinstantsfor step 2:
+      2. Let _list_ be ? IterableToList(_possibleInstants_).
+includes: [temporalHelpers.js]
+---*/
+
+const expected = [
+  "2005-09-09T01:46:40",
+];
+
+TemporalHelpers.checkTimeZonePossibleInstantsIterable((timeZone) => {
+  const datetime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, timeZone);
+  datetime.with({ year: 2005 });
+}, expected);
diff --git a/polyfill/test/helpers/temporalHelpers.js b/polyfill/test/helpers/temporalHelpers.js
index 4975fee94b..005539c362 100644
--- a/polyfill/test/helpers/temporalHelpers.js
+++ b/polyfill/test/helpers/temporalHelpers.js
@@ -374,6 +374,79 @@ var TemporalHelpers = {
     resultAssertions(result);
   },
 
+  /*
+   * Check that any iterable returned from a custom time zone's
+   * getPossibleInstantsFor() method is exhausted.
+   * The custom time zone object is passed in to func().
+   * expected is an array of strings representing the expected calls to the
+   * getPossibleInstantsFor() method. The PlainDateTimes that it is called with,
+   * are compared (using their toString() results) with the array.
+   */
+  checkTimeZonePossibleInstantsIterable(func, expected) {
+    // A custom time zone that returns an iterable instead of an array from its
+    // getPossibleInstantsFor() method, and for testing purposes skips
+    // 00:00-01:00 UTC on January 1, 2030, and repeats 00:00-01:00 UTC+1 on
+    // January 3, 2030. Otherwise identical to the UTC time zone.
+    class TimeZonePossibleInstantsIterable extends Temporal.TimeZone {
+      constructor() {
+        super("UTC");
+        this.getPossibleInstantsForCallCount = 0;
+        this.getPossibleInstantsForCalledWith = [];
+        this.getPossibleInstantsForReturns = [];
+        this.iteratorExhausted = [];
+      }
+
+      toString() {
+        return "Custom/Iterable";
+      }
+
+      getOffsetNanosecondsFor(instant) {
+        if (Temporal.Instant.compare(instant, "2030-01-01T00:00Z") >= 0 &&
+          Temporal.Instant.compare(instant, "2030-01-03T01:00Z") < 0) {
+          return 3600_000_000_000;
+        } else {
+          return 0;
+        }
+      }
+
+      getPossibleInstantsFor(dateTime) {
+        this.getPossibleInstantsForCallCount++;
+        this.getPossibleInstantsForCalledWith.push(dateTime);
+
+        // Fake DST transition
+        let retval = super.getPossibleInstantsFor(dateTime);
+        if (dateTime.toPlainDate().equals("2030-01-01") && dateTime.hour === 0) {
+          retval = [];
+        } else if (dateTime.toPlainDate().equals("2030-01-03") && dateTime.hour === 0) {
+          retval.push(retval[0].subtract({ hours: 1 }));
+        } else if (dateTime.year === 2030 && dateTime.month === 1 && dateTime.day >= 1 && dateTime.day <= 2) {
+          retval[0] = retval[0].subtract({ hours: 1 });
+        }
+
+        this.getPossibleInstantsForReturns.push(retval);
+        this.iteratorExhausted.push(false);
+        return {
+          callIndex: this.getPossibleInstantsForCallCount - 1,
+          timeZone: this,
+          *[Symbol.iterator]() {
+            yield* this.timeZone.getPossibleInstantsForReturns[this.callIndex];
+            this.timeZone.iteratorExhausted[this.callIndex] = true;
+          },
+        };
+      }
+    }
+
+    const timeZone = new TimeZonePossibleInstantsIterable();
+    func(timeZone);
+
+    assert.sameValue(timeZone.getPossibleInstantsForCallCount, expected.length, "getPossibleInstantsFor() method called correct number of times");
+
+    for (let index = 0; index < expected.length; index++) {
+      assert.sameValue(timeZone.getPossibleInstantsForCalledWith[index].toString(), expected[index], "getPossibleInstantsFor() called with expected PlainDateTime");
+      assert(timeZone.iteratorExhausted[index], "iterated through the whole iterable");
+    }
+  },
+
   /*
    * Check that any calendar-carrying Temporal object has its [[Calendar]]
    * internal slot read by ToTemporalCalendar, and does not fetch the calendar