diff --git a/test/staging/Intl402/Temporal/old/islamic-calendars.js b/test/staging/Intl402/Temporal/old/islamic-calendars.js
index 34ff2755f0d..d028463a582 100644
--- a/test/staging/Intl402/Temporal/old/islamic-calendars.js
+++ b/test/staging/Intl402/Temporal/old/islamic-calendars.js
@@ -12,12 +12,27 @@ features: [Temporal]
 const tests = [
   {
     calendar: "islamic",
-    inLeapYear: false,
-    daysInYear: 354,
-    daysInMonth12: 29,
-    isoYear: 2023,
-    isoMonth: 7,
-    isoDay: 18
+    choices: [
+      // Approximations of the observational Islamic calendar as computed by ICU4C.
+      {
+        inLeapYear: false,
+        daysInYear: 354,
+        daysInMonth12: 29,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 18
+      },
+
+      // Approximations of the observational Islamic calendar as computed by ICU4X.
+      {
+        inLeapYear: true,
+        daysInYear: 355,
+        daysInMonth12: 30,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 19
+      }
+    ],
   },
   {
     calendar: "islamic-umalqura",
@@ -48,12 +63,27 @@ const tests = [
   },
   {
     calendar: "islamic-rgsa",
-    inLeapYear: false,
-    daysInYear: 354,
-    daysInMonth12: 29,
-    isoYear: 2023,
-    isoMonth: 7,
-    isoDay: 18
+    choices: [
+      // Approximations of the observational Islamic calendar as computed by ICU4C.
+      {
+        inLeapYear: false,
+        daysInYear: 354,
+        daysInMonth12: 29,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 18
+      },
+
+      // Approximations of the observational Islamic calendar as computed by ICU4X.
+      {
+        inLeapYear: true,
+        daysInYear: 355,
+        daysInMonth12: 30,
+        isoYear: 2023,
+        isoMonth: 7,
+        isoDay: 19
+      }
+    ],
   },
   {
     calendar: "islamic-tbla",
@@ -67,15 +97,29 @@ const tests = [
 ];
 
 for (const test of tests) {
-  const { calendar, inLeapYear, daysInYear, daysInMonth12, isoYear, isoMonth, isoDay } = test;
+  const { calendar, choices = [test] } = test;
   const year = 1445;
   const date = Temporal.PlainDate.from({ year, month: 1, day: 1, calendar });
   const isoFields = date.getISOFields();
-  assert.sameValue(date.calendarId, calendar);
+  if (calendar !== "islamicc") {
+    assert.sameValue(date.calendarId, calendar);
+  } else {
+    // TODO: Steps to canonicalize the calendar identifier are still missing.
+    // https://github.com/tc39/ecma402/issues/828
+  }
   assert.sameValue(date.year, year);
   assert.sameValue(date.month, 1);
   assert.sameValue(date.monthCode, "M01");
   assert.sameValue(date.day, 1);
+
+  // Match the possible choice by comparing the ISO month and day values.
+  const choice = choices.find(({ isoMonth, isoDay }) => {
+    return isoFields.isoMonth === isoMonth && isoFields.isoDay === isoDay;
+  });
+  assert(choice !== undefined, `No applicable choice found for calendar: ${calendar}`);
+
+  const { inLeapYear, daysInYear, daysInMonth12, isoYear, isoMonth, isoDay } = choice;
+
   assert.sameValue(date.inLeapYear, inLeapYear);
   assert.sameValue(date.daysInYear, daysInYear);
   assert.sameValue(date.monthsInYear, 12);