diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
index e9f24c4463..b05c3b701c 100644
--- a/polyfill/lib/ecmascript.mjs
+++ b/polyfill/lib/ecmascript.mjs
@@ -437,23 +437,11 @@ export function ParseISODateTime(isoString) {
   if (match[13]) {
     offset = undefined;
     z = true;
-  } else if (match[14] && match[15]) {
-    const offsetSign = match[14] === '-' || match[14] === '\u2212' ? '-' : '+';
-    const offsetHours = match[15] || '00';
-    const offsetMinutes = match[16] || '00';
-    const offsetSeconds = match[17] || '00';
-    let offsetFraction = match[18] || '0';
-    offset = `${offsetSign}${offsetHours}:${offsetMinutes}`;
-    if (+offsetFraction) {
-      while (offsetFraction.endsWith('0')) offsetFraction = offsetFraction.slice(0, -1);
-      offset += `:${offsetSeconds}.${offsetFraction}`;
-    } else if (+offsetSeconds) {
-      offset += `:${offsetSeconds}`;
-    }
-    if (offset === '-00:00') offset = '+00:00';
+  } else if (match[14]) {
+    offset = match[14];
   }
-  const tzName = match[19];
-  const calendar = processAnnotations(match[20]);
+  const tzName = match[15];
+  const calendar = processAnnotations(match[16]);
   RejectDateTime(year, month, day, hour, minute, second, millisecond, microsecond, nanosecond);
   return {
     year,
@@ -505,7 +493,7 @@ export function ParseTemporalTimeString(isoString) {
     millisecond = ToIntegerOrInfinity(fraction.slice(0, 3));
     microsecond = ToIntegerOrInfinity(fraction.slice(3, 6));
     nanosecond = ToIntegerOrInfinity(fraction.slice(6, 9));
-    processAnnotations(match[14]); // ignore found calendar
+    processAnnotations(match[10]); // ignore found calendar
     if (match[8]) throw new RangeError('Z designator not supported for PlainTime');
   } else {
     let z, hasTime;
@@ -2624,7 +2612,7 @@ export function IsOffsetTimeZoneIdentifier(string) {
 }
 
 export function ParseDateTimeUTCOffset(string) {
-  const match = OFFSET.exec(string);
+  const match = OFFSET_WITH_PARTS.exec(string);
   if (!match) {
     throw new RangeError(`invalid time zone offset: ${string}`);
   }
@@ -5632,6 +5620,7 @@ export function ASCIILowercase(str) {
 }
 
 const OFFSET = new RegExp(`^${PARSE.offset.source}$`);
+const OFFSET_WITH_PARTS = new RegExp(`^${PARSE.offsetWithParts.source}$`);
 
 function bisect(getState, left, right, lstate = getState(left), rstate = getState(right)) {
   left = bigInt(left);
diff --git a/polyfill/lib/regex.mjs b/polyfill/lib/regex.mjs
index 8a71c63841..62658f7f6e 100644
--- a/polyfill/lib/regex.mjs
+++ b/polyfill/lib/regex.mjs
@@ -22,7 +22,9 @@ export const datesplit = new RegExp(
   `(${yearpart.source})(?:-(${monthpart.source})-(${daypart.source})|(${monthpart.source})(${daypart.source}))`
 );
 const timesplit = /(\d{2})(?::(\d{2})(?::(\d{2})(?:[.,](\d{1,9}))?)?|(\d{2})(?:(\d{2})(?:[.,](\d{1,9}))?)?)?/;
-export const offset = /([+\u2212-])([01][0-9]|2[0-3])(?::?([0-5][0-9])(?::?([0-5][0-9])(?:[.,](\d{1,9}))?)?)?/;
+export const offsetWithParts = /([+\u2212-])([01][0-9]|2[0-3])(?::?([0-5][0-9])(?::?([0-5][0-9])(?:[.,](\d{1,9}))?)?)?/;
+export const offset =
+  /((?:[+\u2212-])(?:[01][0-9]|2[0-3])(?::?(?:[0-5][0-9])(?::?(?:[0-5][0-9])(?:[.,](?:\d{1,9}))?)?)?)/;
 const offsetpart = new RegExp(`([zZ])|${offset.source}?`);
 export const offsetIdentifier = /([+\u2212-])([01][0-9]|2[0-3])(?::?([0-5][0-9])?)?/;
 export const annotation = /\[(!)?([a-z_][a-z0-9_-]*)=([A-Za-z0-9]+(?:-[A-Za-z0-9]+)*)\]/g;
diff --git a/polyfill/test/validStrings.mjs b/polyfill/test/validStrings.mjs
index 3ba6aa9b1f..cec937b68c 100644
--- a/polyfill/test/validStrings.mjs
+++ b/polyfill/test/validStrings.mjs
@@ -6,7 +6,6 @@
 
 import assert from 'assert';
 import * as ES from '../lib/ecmascript.mjs';
-import { Instant } from '../lib/instant.mjs';
 
 const timezoneNames = Intl.supportedValuesOf('timeZone');
 const calendarNames = Intl.supportedValuesOf('calendar');
@@ -249,12 +248,7 @@ const temporalSign = withCode(
 );
 const temporalDecimalFraction = fraction;
 function saveOffset(data, result) {
-  // To canonicalize an offset string that may include nanoseconds, we use GetOffsetStringFor
-  const instant = new Instant(0n);
-  const fakeTimeZone = {
-    getOffsetNanosecondsFor: () => ES.ParseDateTimeUTCOffset(result).offsetNanoseconds
-  };
-  data.offset = ES.GetOffsetStringFor(fakeTimeZone, instant);
+  data.offset = ES.ParseDateTimeUTCOffset(result);
 }
 const utcOffsetSubMinutePrecision = withCode(
   seq(
@@ -468,7 +462,13 @@ function fuzzMode(mode) {
       for (let prop of comparisonItems[mode]) {
         let expected = generatedData[prop];
         if (prop !== 'tzName' && prop !== 'offset' && prop !== 'calendar') expected = expected || 0;
-        assert.equal(parsed[prop], expected, prop);
+        if (prop === 'offset' && expected) {
+          const parsedResult = ES.ParseDateTimeUTCOffset(parsed[prop]);
+          assert.equal(parsedResult.offsetNanoseconds, expected.offsetNanoseconds);
+          assert.equal(parsedResult.hasSubMinutePrecision, expected.hasSubMinutePrecision);
+        } else {
+          assert.equal(parsed[prop], expected, prop);
+        }
       }
       console.log(`${fuzzed} => ok`);
     } catch (e) {
diff --git a/polyfill/test262 b/polyfill/test262
index 29dde1ce0e..66f3959c14 160000
--- a/polyfill/test262
+++ b/polyfill/test262
@@ -1 +1 @@
-Subproject commit 29dde1ce0e97a8bd6423c4397b9d3b51df0a1d8e
+Subproject commit 66f3959c14646a4caba79e91adfe976c28246bf9