diff --git a/test/built-ins/Temporal/Instant/prototype/round/rounding-direction.js b/test/built-ins/Temporal/Instant/prototype/round/rounding-direction.js
new file mode 100644
index 00000000000..88a6abba4c2
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/prototype/round/rounding-direction.js
@@ -0,0 +1,30 @@
+// 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.round
+description: Rounding down is towards the Big Bang, not the epoch or 1 BCE
+features: [Temporal]
+---*/
+
+const instance = new Temporal.Instant(-65_261_246_399_500_000_000n);  // -000099-12-15T12:00:00.5Z
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "floor" }).epochNanoseconds,
+  -65_261_246_400_000_000_000n,  // -000099-12-15T12:00:00Z
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode floor)"
+);
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "trunc" }).epochNanoseconds,
+  -65_261_246_400_000_000_000n,  // -000099-12-15T12:00:00Z
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode trunc)"
+);
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "ceil" }).epochNanoseconds,
+  -65_261_246_399_000_000_000n,  // -000099-12-15T12:00:01Z
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode ceil)"
+);
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "halfExpand" }).epochNanoseconds,
+  -65_261_246_399_000_000_000n,  // -000099-12-15T12:00:01Z
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode halfExpand)"
+);
diff --git a/test/built-ins/Temporal/Instant/prototype/toString/rounding-direction.js b/test/built-ins/Temporal/Instant/prototype/toString/rounding-direction.js
new file mode 100644
index 00000000000..f5185d9331d
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/prototype/toString/rounding-direction.js
@@ -0,0 +1,30 @@
+// 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.tostring
+description: Rounding down is towards the Big Bang, not the epoch or 1 BCE
+features: [Temporal]
+---*/
+
+const instance = new Temporal.Instant(-65_261_246_399_500_000_000n);  // -000099-12-15T12:00:00.5Z
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "floor" }),
+  "-000099-12-15T12:00:00Z",
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "trunc" }),
+  "-000099-12-15T12:00:00Z",
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode trunc)"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "ceil" }),
+  "-000099-12-15T12:00:01Z",
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode ceil)"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "halfExpand" }),
+  "-000099-12-15T12:00:01Z",
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode halfExpand)"
+);
diff --git a/test/built-ins/Temporal/PlainDateTime/prototype/round/rounding-direction.js b/test/built-ins/Temporal/PlainDateTime/prototype/round/rounding-direction.js
new file mode 100644
index 00000000000..5e0e1eaeca4
--- /dev/null
+++ b/test/built-ins/Temporal/PlainDateTime/prototype/round/rounding-direction.js
@@ -0,0 +1,31 @@
+// 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.plaindatetime.prototype.round
+description: Rounding down is towards the Big Bang, not the epoch or 1 BCE
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const instance = new Temporal.PlainDateTime(-99, 12, 15, 12, 0, 0, 500);
+TemporalHelpers.assertPlainDateTime(
+  instance.round({ smallestUnit: "second", roundingMode: "floor" }),
+  -99, 12, "M12", 15, 12, 0, 0, 0, 0, 0,
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode floor)"
+);
+TemporalHelpers.assertPlainDateTime(
+  instance.round({ smallestUnit: "second", roundingMode: "trunc" }),
+  -99, 12, "M12", 15, 12, 0, 0, 0, 0, 0,
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode trunc)"
+);
+TemporalHelpers.assertPlainDateTime(
+  instance.round({ smallestUnit: "second", roundingMode: "ceil" }),
+  -99, 12, "M12", 15, 12, 0, 1, 0, 0, 0,
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode ceil)"
+);
+TemporalHelpers.assertPlainDateTime(
+  instance.round({ smallestUnit: "second", roundingMode: "halfExpand" }),
+  -99, 12, "M12", 15, 12, 0, 1, 0, 0, 0,
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode halfExpand)"
+);
diff --git a/test/built-ins/Temporal/PlainDateTime/prototype/toString/rounding-direction.js b/test/built-ins/Temporal/PlainDateTime/prototype/toString/rounding-direction.js
new file mode 100644
index 00000000000..a4d7dec32d7
--- /dev/null
+++ b/test/built-ins/Temporal/PlainDateTime/prototype/toString/rounding-direction.js
@@ -0,0 +1,30 @@
+// 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.plaindatetime.prototype.tostring
+description: Rounding down is towards the Big Bang, not the epoch or 1 BCE
+features: [Temporal]
+---*/
+
+const instance = new Temporal.PlainDateTime(-99, 12, 15, 12, 0, 0, 500);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "floor" }),
+  "-000099-12-15T12:00:00",
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "trunc" }),
+  "-000099-12-15T12:00:00",
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode trunc)"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "ceil" }),
+  "-000099-12-15T12:00:01",
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode ceil)"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "halfExpand" }),
+  "-000099-12-15T12:00:01",
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode halfExpand)"
+);
diff --git a/test/built-ins/Temporal/ZonedDateTime/prototype/round/rounding-direction.js b/test/built-ins/Temporal/ZonedDateTime/prototype/round/rounding-direction.js
new file mode 100644
index 00000000000..676841ed26d
--- /dev/null
+++ b/test/built-ins/Temporal/ZonedDateTime/prototype/round/rounding-direction.js
@@ -0,0 +1,30 @@
+// 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.zoneddatetime.prototype.round
+description: Rounding down is towards the Big Bang, not the epoch or 1 BCE
+features: [Temporal]
+---*/
+
+const instance = new Temporal.ZonedDateTime(-65_261_246_399_500_000_000n, "UTC");  // -000099-12-15T12:00:00.5Z
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "floor" }).epochNanoseconds,
+  -65_261_246_400_000_000_000n,  // -000099-12-15T12:00:00Z
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode floor)"
+);
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "trunc" }).epochNanoseconds,
+  -65_261_246_400_000_000_000n,  // -000099-12-15T12:00:00Z
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode trunc)"
+);
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "ceil" }).epochNanoseconds,
+  -65_261_246_399_000_000_000n,  // -000099-12-15T12:00:01Z
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode ceil)"
+);
+assert.sameValue(
+  instance.round({ smallestUnit: "second", roundingMode: "halfExpand" }).epochNanoseconds,
+  -65_261_246_399_000_000_000n,  // -000099-12-15T12:00:01Z
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode halfExpand)"
+);
diff --git a/test/built-ins/Temporal/ZonedDateTime/prototype/toString/rounding-direction.js b/test/built-ins/Temporal/ZonedDateTime/prototype/toString/rounding-direction.js
new file mode 100644
index 00000000000..b376e075bb8
--- /dev/null
+++ b/test/built-ins/Temporal/ZonedDateTime/prototype/toString/rounding-direction.js
@@ -0,0 +1,30 @@
+// 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.zoneddatetime.prototype.tostring
+description: Rounding down is towards the Big Bang, not the epoch or 1 BCE
+features: [Temporal]
+---*/
+
+const instance = new Temporal.ZonedDateTime(-65_261_246_399_500_000_000n, "UTC");  // -000099-12-15T12:00:00.5Z
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "floor" }),
+  "-000099-12-15T12:00:00+00:00[UTC]",
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "trunc" }),
+  "-000099-12-15T12:00:00+00:00[UTC]",
+  "Rounding down is towards the Big Bang, not the epoch or 1 BCE (roundingMode trunc)"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "ceil" }),
+  "-000099-12-15T12:00:01+00:00[UTC]",
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode ceil)"
+);
+assert.sameValue(
+  instance.toString({ smallestUnit: "second", roundingMode: "halfExpand" }),
+  "-000099-12-15T12:00:01+00:00[UTC]",
+  "Rounding up is away from the Big Bang, not the epoch or 1 BCE (roundingMode halfExpand)"
+);