diff --git a/test/built-ins/Temporal/Instant/compare/argument-string-invalid.js b/test/built-ins/Temporal/Instant/compare/argument-string-invalid.js
new file mode 100644
index 0000000000..1687124307
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/compare/argument-string-invalid.js
@@ -0,0 +1,71 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.instant.compare
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const epoch = new Temporal.Instant(0n);
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => Temporal.Instant.compare(arg, epoch),
+    `"${arg}" should not be a valid ISO string for an Instant (first argument)`
+  );
+  assert.throws(
+    RangeError,
+    () => Temporal.Instant.compare(epoch, arg),
+    `"${arg}" should not be a valid ISO string for an Instant (second argument)`
+  );
+}
diff --git a/test/built-ins/Temporal/Instant/from/argument-string-invalid.js b/test/built-ins/Temporal/Instant/from/argument-string-invalid.js
new file mode 100644
index 0000000000..8797b8ed01
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/from/argument-string-invalid.js
@@ -0,0 +1,64 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.instant.from
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => Temporal.Instant.from(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/Instant/prototype/equals/argument-string-invalid.js b/test/built-ins/Temporal/Instant/prototype/equals/argument-string-invalid.js
new file mode 100644
index 0000000000..581de1c51b
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/prototype/equals/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.instant.prototype.equals
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.Instant(0n);
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.equals(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/Instant/prototype/since/argument-string-invalid.js b/test/built-ins/Temporal/Instant/prototype/since/argument-string-invalid.js
new file mode 100644
index 0000000000..9ce112b73f
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/prototype/since/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.instant.prototype.since
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.Instant(0n);
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.since(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/Instant/prototype/until/argument-string-invalid.js b/test/built-ins/Temporal/Instant/prototype/until/argument-string-invalid.js
new file mode 100644
index 0000000000..96585258d7
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/prototype/until/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.instant.prototype.until
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.Instant(0n);
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.until(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/TimeZone/prototype/getNextTransition/argument-string-invalid.js b/test/built-ins/Temporal/TimeZone/prototype/getNextTransition/argument-string-invalid.js
new file mode 100644
index 0000000000..934edbfdf6
--- /dev/null
+++ b/test/built-ins/Temporal/TimeZone/prototype/getNextTransition/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.timezone.prototype.getnexttransition
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.TimeZone("UTC");
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.getNextTransition(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/TimeZone/prototype/getOffsetNanosecondsFor/argument-string-invalid.js b/test/built-ins/Temporal/TimeZone/prototype/getOffsetNanosecondsFor/argument-string-invalid.js
new file mode 100644
index 0000000000..7780706e02
--- /dev/null
+++ b/test/built-ins/Temporal/TimeZone/prototype/getOffsetNanosecondsFor/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.timezone.prototype.getoffsetnanosecondsfor
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.TimeZone("UTC");
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.getOffsetNanosecondsFor(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/TimeZone/prototype/getOffsetStringFor/argument-string-invalid.js b/test/built-ins/Temporal/TimeZone/prototype/getOffsetStringFor/argument-string-invalid.js
new file mode 100644
index 0000000000..f3c2d26693
--- /dev/null
+++ b/test/built-ins/Temporal/TimeZone/prototype/getOffsetStringFor/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.timezone.prototype.getoffsetstringfor
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.TimeZone("UTC");
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.getOffsetStringFor(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/TimeZone/prototype/getPlainDateTimeFor/argument-string-invalid.js b/test/built-ins/Temporal/TimeZone/prototype/getPlainDateTimeFor/argument-string-invalid.js
new file mode 100644
index 0000000000..8d114f824e
--- /dev/null
+++ b/test/built-ins/Temporal/TimeZone/prototype/getPlainDateTimeFor/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.timezone.prototype.getplaindatetimefor
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.TimeZone("UTC");
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.getPlainDateTimeFor(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}
diff --git a/test/built-ins/Temporal/TimeZone/prototype/getPreviousTransition/argument-string-invalid.js b/test/built-ins/Temporal/TimeZone/prototype/getPreviousTransition/argument-string-invalid.js
new file mode 100644
index 0000000000..3b83ea8c35
--- /dev/null
+++ b/test/built-ins/Temporal/TimeZone/prototype/getPreviousTransition/argument-string-invalid.js
@@ -0,0 +1,66 @@
+// Copyright (C) 2022 Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.timezone.prototype.getprevioustransition
+description: >
+  RangeError thrown if an invalid ISO string (or syntactically valid ISO string
+  that is not supported) is used as an Instant
+features: [Temporal, arrow-function]
+---*/
+
+const invalidStrings = [
+  // invalid ISO strings:
+  "",
+  "invalid iso8601",
+  "2020-01-00T00:00Z",
+  "2020-01-32T00:00Z",
+  "2020-02-30T00:00Z",
+  "2021-02-29T00:00Z",
+  "2020-00-01T00:00Z",
+  "2020-13-01T00:00Z",
+  "2020-01-01TZ",
+  "2020-01-01T25:00:00Z",
+  "2020-01-01T01:60:00Z",
+  "2020-01-01T01:60:61Z",
+  "2020-01-01T00:00Zjunk",
+  "2020-01-01T00:00:00Zjunk",
+  "2020-01-01T00:00:00.000000000Zjunk",
+  "2020-01-01T00:00:00+00:00junk",
+  "2020-01-01T00:00:00+00:00[UTC]junk",
+  "2020-01-01T00:00:00+00:00[UTC][u-ca=iso8601]junk",
+  "02020-01-01T00:00Z",
+  "2020-001-01T00:00Z",
+  "2020-01-001T00:00Z",
+  "2020-01-01T001Z",
+  "2020-01-01T01:001Z",
+  "2020-01-01T01:01:001Z",
+  // valid, but forms not supported in Temporal:
+  "2020-W01-1T00:00Z",
+  "2020-001T00:00Z",
+  "+0002020-01-01T00:00Z",
+  // may be valid in other contexts, but insufficient information for Instant:
+  "2020-01",
+  "+002020-01",
+  "01-01",
+  "2020-W01",
+  "P1Y",
+  "-P12Y",
+  "2020-01-01",
+  "2020-01-01T00",
+  "2020-01-01T00:00",
+  "2020-01-01T00:00:00",
+  "2020-01-01T00:00:00.000000000",
+  // valid, but outside the supported range:
+  "-999999-01-01T00:00Z",
+  "+999999-01-01T00:00Z",
+];
+
+const instance = new Temporal.TimeZone("UTC");
+for (const arg of invalidStrings) {
+  assert.throws(
+    RangeError,
+    () => instance.getPreviousTransition(arg),
+    `"${arg}" should not be a valid ISO string for an Instant`
+  );
+}