diff --git a/test/intl402/Temporal/ZonedDateTime/prototype/getTimeZoneTransition/transitions-close-together.js b/test/intl402/Temporal/ZonedDateTime/prototype/getTimeZoneTransition/transitions-close-together.js
new file mode 100644
index 0000000000..ca668320cb
--- /dev/null
+++ b/test/intl402/Temporal/ZonedDateTime/prototype/getTimeZoneTransition/transitions-close-together.js
@@ -0,0 +1,46 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.zoneddatetime.prototype.gettimezonetransition
+description: Test TZDB edge case where transitions occur close together
+features: [Temporal]
+---*/
+
+// This is a list of time zones that have transitions occurring less than two
+// weeks apart. (Some additional ones occur in questionable future calculations
+// which are not included here.)
+// Implementations using a bisect strategy to find the transition times, must
+// use a small enough window to catch these transitions.
+
+const testData = {
+  "Africa/Tunis": [-842918400n /* 1943-04-17T01+01:00 */, -842223600n /* 1943-04-25T03+02:00 */],
+  "America/Argentina/Tucuman": [1086058800n /* 2004-05-31T23-04:00 */, 1087099200n /* 2004-06-13T01-03:00 */],
+  "America/Boa_Vista": [970977600n /* 2000-10-08T01-03:00 */, 971578800n /* 2000-10-14T23-04:00 */],
+  "America/Fortaleza": [970974000n /* 2000-10-08T01-02:00 */, 972180000n /* 2000-10-21T23-03:00 */],
+  "America/Maceio": [970974000n /* 2000-10-08T01-02:00 */, 972180000n /* 2000-10-21T23-03:00 */],
+  "America/Noronha": [970970400n /* 2000-10-08T01-01:00 */, 971571600n /* 2000-10-14T23-02:00 */],
+  "America/Recife": [970974000n /* 2000-10-08T01-02:00 */, 971575200n /* 2000-10-14T23-03:00 */],
+  "Europe/Riga": [-796777200n /* 1944-10-02T02+01:00 */, -795834000n /* 1944-10-13T02+03:00 */],
+  "Europe/Simferopol": [-812502000n /* 1944-04-03T03+02:00 */, -811648800n /* 1944-04-13T01+03:00 */],
+  "Europe/Tirane": [-844556400n /* 1943-03-29T03+02:00 */, -843519600n /* 1943-04-10T02+01:00 */],
+  "Europe/Vienna": [-781052400n /* 1945-04-02T03+02:00 */, -780188400n /* 1945-04-12T02+01:00 */],
+}
+
+for (const [zone, [first, second]] of Object.entries(testData)) {
+  for (const [label, epochSeconds] of Object.entries({ first, second }) ) {
+    const transition = new Temporal.ZonedDateTime(epochSeconds * 1_000_000_000n, zone);
+    const before = new Temporal.ZonedDateTime((epochSeconds - 1800n) * 1_000_000_000n, zone);
+    const after = new Temporal.ZonedDateTime((epochSeconds + 1800n) * 1_000_000_000n, zone);
+
+    assert.sameValue(
+      before.getTimeZoneTransition("next").epochNanoseconds,
+      transition.epochNanoseconds,
+      `${zone} offset transitions close together, next to ${label} transition`
+    );
+    assert.sameValue(
+      after.getTimeZoneTransition("previous").epochNanoseconds,
+      transition.epochNanoseconds,
+      `${zone} offset transitions close together, previous to ${label} transition`
+    );
+  }
+}
diff --git a/test/intl402/Temporal/ZonedDateTime/prototype/startOfDay/transitions-close-together.js b/test/intl402/Temporal/ZonedDateTime/prototype/startOfDay/transitions-close-together.js
new file mode 100644
index 0000000000..57c216c165
--- /dev/null
+++ b/test/intl402/Temporal/ZonedDateTime/prototype/startOfDay/transitions-close-together.js
@@ -0,0 +1,40 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-temporal.zoneddatetime.prototype.startofday
+description: Test TZDB edge case where transitions occur close together
+features: [Temporal]
+---*/
+
+// Zone America/Noronha (Fernando de Noronha) switched to DST -01:00 according
+// to the Brazilian DST rules then in effect on 2000-10-08T00. Then the
+// following week on 2000-10-15T00 discarded DST, going back to a permanent
+// -02:00 offset. Implementations using a bisect method to find the transition
+// times, must use a small enough window to catch these transitions 1 week
+// apart.
+
+const noronha = new Temporal.ZonedDateTime(970970400000000000n /* 2000-10-08T01-01:00 */, "America/Noronha");
+
+assert.sameValue(
+  noronha.startOfDay().epochNanoseconds,
+  noronha.epochNanoseconds,
+  "America/Noronha offset transitions close together"
+);
+
+// Same deal for zone America/Boa_Vista, but with -03:00 and -04:00
+// respectively. Test again with an instance that is not already the start of
+// the day.
+
+const boaVistaStart = new Temporal.ZonedDateTime(970977600000000000n /* 2000-10-08T01-03:00 */, "America/Boa_Vista");
+const boaVista = new Temporal.ZonedDateTime(970984800000000000n /* 2000-10-08T03-03:00 */, "America/Boa_Vista");
+
+assert.sameValue(
+  boaVista.startOfDay().epochNanoseconds,
+  boaVistaStart.epochNanoseconds,
+  "America/Boa_Vista offset transitions close together"
+);
+
+// The same thing occurs in several other Brazilian time zones on the same or
+// nearby dates, but these two are sufficient for the test. Other occur at other
+// times of the day (see ../getTimeZoneTransition/transitions-close-together.js)
+// but those are not relevant for startOfDay().