diff --git a/harness/temporalHelpers.js b/harness/temporalHelpers.js
index 6aba4a03cf..b4c0fb1604 100644
--- a/harness/temporalHelpers.js
+++ b/harness/temporalHelpers.js
@@ -1197,6 +1197,8 @@ var TemporalHelpers = {
         "1976-11[U-CA=iso8601]",
         "1976-11[u-CA=iso8601]",
         "1976-11[FOO=bar]",
+        "+999999-01",
+        "-999999-01",
       ];
     },
 
diff --git a/test/built-ins/Temporal/PlainYearMonth/argument-invalid.js b/test/built-ins/Temporal/PlainYearMonth/argument-invalid.js
new file mode 100644
index 0000000000..7ccc20e375
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/argument-invalid.js
@@ -0,0 +1,24 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth
+description: PlainYearMonth constructor with invalid iso dates
+features: [Temporal]
+---*/
+
+const tests = [
+  [2020, 0, 24],
+  [2020, 13, 24],
+  [2020, -3, 24],
+  [2020, 12, 32],
+  [2020, 2, 30],
+  [2019, 2, 29],
+  [2019, 2, 0],
+  [2019, 2, -20],
+];
+
+for (const [year, month, day] of tests) {
+  assert.throws(RangeError, () => new Temporal.PlainYearMonth(year, month, undefined, day),
+    `year=${year}, month=${month}, day=${day}`);
+}
diff --git a/test/built-ins/Temporal/PlainYearMonth/get-prototype-from-constructor-throws.js b/test/built-ins/Temporal/PlainYearMonth/get-prototype-from-constructor-throws.js
new file mode 100644
index 0000000000..cfbc0ade8e
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/get-prototype-from-constructor-throws.js
@@ -0,0 +1,40 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth
+description: >
+  OrdinaryCreateFromConstructor returns with an abrupt completion.
+info: |
+  CreateTemporalYearMonth ( isoDate, calendar [ , newTarget ] )
+
+  ...
+  3. Let object be ? OrdinaryCreateFromConstructor(newTarget,
+     "%Temporal.PlainYearMonth.prototype%", « [[InitializedTemporalYearMonth]],
+     [[ISODate]], [[Calendar]] »).
+  ...
+
+  OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto [ , internalSlotsList ] )
+
+  ...
+  2. Let proto be ? GetPrototypeFromConstructor(constructor, intrinsicDefaultProto).
+  ...
+
+  GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto )
+
+  ...
+  2. Let proto be ? Get(constructor, "prototype").
+  ...
+
+features: [Temporal]
+---*/
+
+var newTarget = Object.defineProperty(function(){}.bind(), "prototype", {
+  get() {
+    throw new Test262Error();
+  }
+});
+
+assert.throws(Test262Error, function() {
+  Reflect.construct(Temporal.PlainYearMonth, [1, 1], newTarget)
+});
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/add/throws-if-year-outside-valid-iso-range.js b/test/built-ins/Temporal/PlainYearMonth/prototype/add/throws-if-year-outside-valid-iso-range.js
new file mode 100644
index 0000000000..694c0c6b0d
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/add/throws-if-year-outside-valid-iso-range.js
@@ -0,0 +1,27 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.add
+description: >
+  Throws if thisFields is not within valid ISO date range.
+info: |
+  Temporal.PlainYearMonth.prototype.add ( temporalDurationLike [ , options ] )
+
+  ...
+  3. Return ? AddDurationToYearMonth(add, yearMonth, temporalDurationLike, options).
+
+  AddDurationToYearMonth ( operation, yearMonth, temporalDurationLike, options )
+
+  ...
+  8. Set fields.[[Day]] to 1.
+  9. Let intermediateDate be ? CalendarDateFromFields(calendar, fields, constrain).
+  ...
+
+features: [Temporal]
+---*/
+
+const minYearMonth = new Temporal.PlainYearMonth(-271821, 4);
+const blank = new Temporal.Duration();
+
+assert.throws(RangeError, () => minYearMonth.add(blank));
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/since/throws-if-rounded-date-outside-valid-iso-range.js b/test/built-ins/Temporal/PlainYearMonth/prototype/since/throws-if-rounded-date-outside-valid-iso-range.js
new file mode 100644
index 0000000000..ccf6a29d90
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/since/throws-if-rounded-date-outside-valid-iso-range.js
@@ -0,0 +1,47 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.since
+description: >
+  Throws if rounded date outside valid ISO date range.
+info: |
+  Temporal.PlainYearMonth.prototype.since ( other [ , options ] )
+
+  ...
+  3. Return ? DifferenceTemporalPlainYearMonth(since, yearMonth, other, options).
+
+  DifferenceTemporalPlainYearMonth ( operation, yearMonth, other, options )
+
+  ...
+  16. If settings.[[SmallestUnit]] is not month or settings.[[RoundingIncrement]] ≠ 1, then
+    ...
+    d. Set duration to ? RoundRelativeDuration(duration, destEpochNs, isoDateTime,
+       unset, calendar, settings.[[LargestUnit]], settings.[[RoundingIncrement]],
+       settings.[[SmallestUnit]], settings.[[RoundingMode]]).[[Duration]].
+  ...
+
+  RoundRelativeDuration ( duration, destEpochNs, isoDateTime, timeZone, calendar,
+                          largestUnit, increment, smallestUnit, roundingMode )
+
+  ...
+  5. If irregularLengthUnit is true, then
+    a. Let record be ? NudgeToCalendarUnit(sign, duration, destEpochNs, isoDateTime,
+       timeZone, calendar, increment, smallestUnit, roundingMode).
+    ...
+
+  NudgeToCalendarUnit ( sign, duration, destEpochNs, isoDateTime, timeZone, calendar,
+                        increment, unit, roundingMode )
+
+  ...
+  8. Let end be ? CalendarDateAdd(calendar, isoDateTime.[[ISODate]], endDuration, constrain).
+  ...
+
+features: [Temporal]
+---*/
+
+var from = new Temporal.PlainYearMonth(1970, 1);
+var to = new Temporal.PlainYearMonth(1971, 1);
+var options = {roundingIncrement: 100_000_000};
+
+assert.throws(RangeError, () => from.since(to, options));
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/since/throws-if-year-outside-valid-iso-range.js b/test/built-ins/Temporal/PlainYearMonth/prototype/since/throws-if-year-outside-valid-iso-range.js
new file mode 100644
index 0000000000..33e841b91e
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/since/throws-if-year-outside-valid-iso-range.js
@@ -0,0 +1,45 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.since
+description: >
+  Throws if thisFields is not within valid ISO date range.
+info: |
+  Temporal.PlainYearMonth.prototype.since ( other [ , options ] )
+
+  ...
+  3. Return ? DifferenceTemporalPlainYearMonth(since, yearMonth, other, options).
+
+  DifferenceTemporalPlainYearMonth ( operation, yearMonth, other, options )
+
+  ...
+  8. Set thisFields.[[Day]] to 1.
+  9. Let thisDate be ? CalendarDateFromFields(calendar, thisFields, constrain).
+  ...
+
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const minYearMonth = new Temporal.PlainYearMonth(-271821, 4);
+const maxYearMonth = new Temporal.PlainYearMonth(275760, 9);
+const epochYearMonth = new Temporal.PlainYearMonth(1970, 1);
+
+TemporalHelpers.assertDuration(
+  minYearMonth.since(minYearMonth),
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+  "minYearMonth.since(minYearMonth)"
+);
+
+assert.throws(
+  RangeError,
+  () => minYearMonth.since(maxYearMonth),
+  "minYearMonth.since(maxYearMonth)"
+);
+
+assert.throws(
+  RangeError,
+  () => minYearMonth.since(epochYearMonth),
+  "minYearMonth.since(epochYearMonth)"
+);
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/subtract/throws-if-year-outside-valid-iso-range.js b/test/built-ins/Temporal/PlainYearMonth/prototype/subtract/throws-if-year-outside-valid-iso-range.js
new file mode 100644
index 0000000000..1234f12bb7
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/subtract/throws-if-year-outside-valid-iso-range.js
@@ -0,0 +1,27 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.subtract
+description: >
+  Throws if thisFields is not within valid ISO date range.
+info: |
+  Temporal.PlainYearMonth.prototype.subtract ( temporalDurationLike [ , options ] )
+
+  ...
+  3. Return ? AddDurationToYearMonth(subtract, yearMonth, temporalDurationLike, options).
+
+  AddDurationToYearMonth ( operation, yearMonth, temporalDurationLike, options )
+
+  ...
+  8. Set fields.[[Day]] to 1.
+  9. Let intermediateDate be ? CalendarDateFromFields(calendar, fields, constrain).
+  ...
+
+features: [Temporal]
+---*/
+
+const minYearMonth = new Temporal.PlainYearMonth(-271821, 4);
+const blank = new Temporal.Duration();
+
+assert.throws(RangeError, () => minYearMonth.subtract(blank));
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/toJSON/basic.js b/test/built-ins/Temporal/PlainYearMonth/prototype/toJSON/basic.js
new file mode 100644
index 0000000000..0c23a684e8
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/toJSON/basic.js
@@ -0,0 +1,22 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.tojson
+description: Basic behavior for toJSON
+features: [Temporal]
+---*/
+
+const tests = [
+  [new Temporal.PlainYearMonth(1972, 1), "1972-01"],
+  [new Temporal.PlainYearMonth(1972, 12), "1972-12"],
+];
+
+const options = new Proxy({}, {
+  get() { throw new Test262Error("should not get properties off argument") }
+});
+
+for (const [yearMonth, expected] of tests) {
+  assert.sameValue(yearMonth.toJSON(), expected, "toJSON without argument");
+  assert.sameValue(yearMonth.toJSON(options), expected, "toJSON with argument");
+}
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/return-string.js b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/return-string.js
new file mode 100644
index 0000000000..92ff7d0138
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/return-string.js
@@ -0,0 +1,15 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.tolocalestring
+description: toLocaleString returns a string.
+features: [Temporal]
+---*/
+
+const pym = new Temporal.PlainYearMonth(1, 1);
+
+assert.sameValue(
+  typeof pym.toLocaleString(undefined, {calendar: "iso8601"}),
+  "string"
+);
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/until/throws-if-rounded-date-outside-valid-iso-range.js b/test/built-ins/Temporal/PlainYearMonth/prototype/until/throws-if-rounded-date-outside-valid-iso-range.js
new file mode 100644
index 0000000000..070ed2fd7c
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/until/throws-if-rounded-date-outside-valid-iso-range.js
@@ -0,0 +1,47 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.until
+description: >
+  Throws if rounded date outside valid ISO date range.
+info: |
+  Temporal.PlainYearMonth.prototype.until ( other [ , options ] )
+
+  ...
+  3. Return ? DifferenceTemporalPlainYearMonth(until, yearMonth, other, options).
+
+  DifferenceTemporalPlainYearMonth ( operation, yearMonth, other, options )
+
+  ...
+  16. If settings.[[SmallestUnit]] is not month or settings.[[RoundingIncrement]] ≠ 1, then
+    ...
+    d. Set duration to ? RoundRelativeDuration(duration, destEpochNs, isoDateTime,
+       unset, calendar, settings.[[LargestUnit]], settings.[[RoundingIncrement]],
+       settings.[[SmallestUnit]], settings.[[RoundingMode]]).[[Duration]].
+  ...
+
+  RoundRelativeDuration ( duration, destEpochNs, isoDateTime, timeZone, calendar,
+                          largestUnit, increment, smallestUnit, roundingMode )
+
+  ...
+  5. If irregularLengthUnit is true, then
+    a. Let record be ? NudgeToCalendarUnit(sign, duration, destEpochNs, isoDateTime,
+       timeZone, calendar, increment, smallestUnit, roundingMode).
+    ...
+
+  NudgeToCalendarUnit ( sign, duration, destEpochNs, isoDateTime, timeZone, calendar,
+                        increment, unit, roundingMode )
+
+  ...
+  8. Let end be ? CalendarDateAdd(calendar, isoDateTime.[[ISODate]], endDuration, constrain).
+  ...
+
+features: [Temporal]
+---*/
+
+var from = new Temporal.PlainYearMonth(1970, 1);
+var to = new Temporal.PlainYearMonth(1971, 1);
+var options = {roundingIncrement: 100_000_000};
+
+assert.throws(RangeError, () => from.until(to, options));
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/until/throws-if-year-outside-valid-iso-range.js b/test/built-ins/Temporal/PlainYearMonth/prototype/until/throws-if-year-outside-valid-iso-range.js
new file mode 100644
index 0000000000..1cf376b31a
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/until/throws-if-year-outside-valid-iso-range.js
@@ -0,0 +1,45 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.until
+description: >
+  Throws if thisFields is not within valid ISO date range.
+info: |
+  Temporal.PlainYearMonth.prototype.until ( other [ , options ] )
+
+  ...
+  3. Return ? DifferenceTemporalPlainYearMonth(until, yearMonth, other, options).
+
+  DifferenceTemporalPlainYearMonth ( operation, yearMonth, other, options )
+
+  ...
+  8. Set thisFields.[[Day]] to 1.
+  9. Let thisDate be ? CalendarDateFromFields(calendar, thisFields, constrain).
+  ...
+
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const minYearMonth = new Temporal.PlainYearMonth(-271821, 4);
+const maxYearMonth = new Temporal.PlainYearMonth(275760, 9);
+const epochYearMonth = new Temporal.PlainYearMonth(1970, 1);
+
+TemporalHelpers.assertDuration(
+  minYearMonth.until(minYearMonth),
+  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+  "minYearMonth.until(minYearMonth)"
+);
+
+assert.throws(
+  RangeError,
+  () => minYearMonth.until(maxYearMonth),
+  "minYearMonth.until(maxYearMonth)"
+);
+
+assert.throws(
+  RangeError,
+  () => minYearMonth.until(epochYearMonth),
+  "minYearMonth.until(epochYearMonth)"
+);
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/with/yearmonthlike-invalid.js b/test/built-ins/Temporal/PlainYearMonth/prototype/with/yearmonthlike-invalid.js
new file mode 100644
index 0000000000..8aeb93f042
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/with/yearmonthlike-invalid.js
@@ -0,0 +1,58 @@
+// Copyright (C) 2024 André Bargull. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: >
+  Throws TypeError on an argument that is not a PlainYearMonth-like property bag
+info: |
+  Temporal.PlainYearMonth.prototype.with ( temporalYearMonthLike [ , options ] )
+
+  ...
+  3. If ? IsPartialTemporalObject(temporalYearMonthLike) is false, throw a TypeError exception.
+  ...
+  6. Let partialYearMonth be ? PrepareCalendarFields(calendar, temporalYearMonthLike, « year, month, month-code », « », partial).
+  ...
+features: [Temporal]
+---*/
+
+const plainYearMonth = new Temporal.PlainYearMonth(1, 1);
+
+const tests = [
+  // Step 3.
+  // IsPartialTemporalObject, step 1.
+  [undefined],
+  [null],
+  [true],
+  ["2019-05-17"],
+  ["2019-05-17T12:34"],
+  ["2019-05-17T12:34Z"],
+  ["18:05:42.577"],
+  ["42"],
+  [Symbol(), "symbol"],
+  [42, "number"],
+  [42n, "bigint"],
+
+  // IsPartialTemporalObject, step 2.
+  [Temporal.PlainDate.from("2019-05-17"), "PlainDate"],
+  [Temporal.PlainDateTime.from("2019-05-17T12:34"), "PlainDateTime"],
+  [Temporal.PlainMonthDay.from("2019-05-17"), "PlainMonthDay"],
+  [Temporal.PlainTime.from("12:34"), "PlainTime"],
+  [Temporal.PlainYearMonth.from("2019-05-17"), "PlainYearMonth"],
+  [Temporal.ZonedDateTime.from("2019-05-17T12:34Z[UTC]"), "ZonedDateTime"],
+
+  // IsPartialTemporalObject, step 3.
+  [{ year: 2021, calendar: "iso8601" }, "calendar"],
+
+  // IsPartialTemporalObject, step 4.
+  [{ year: 2021, timeZone: "UTC" }, "timeZone"],
+
+  // Step 6.
+  // PrepareCalendarFields, step 10.
+  [{}, "empty object"],
+  [{ months: 12 }, "only plural property"],
+];
+
+for (const [value, message = String(value)] of tests) {
+  assert.throws(TypeError, () => plainYearMonth.with(value), message);
+}