diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
index 2fdde44e85..b42e25c834 100644
--- a/polyfill/lib/ecmascript.mjs
+++ b/polyfill/lib/ecmascript.mjs
@@ -5088,15 +5088,9 @@ export function RoundDuration(
   relativeTo = undefined
 ) {
   const TemporalDuration = GetIntrinsic('%Temporal.Duration%');
-  let calendar, zdtRelative;
-  if (relativeTo) {
-    if (IsTemporalZonedDateTime(relativeTo)) {
-      zdtRelative = relativeTo;
-      relativeTo = ToTemporalDate(relativeTo);
-    } else if (!IsTemporalDate(relativeTo)) {
-      throw new TypeError('starting point must be PlainDate or ZonedDateTime');
-    }
-    calendar = GetSlot(relativeTo, CALENDAR);
+
+  if ((unit === 'year' || unit === 'month' || unit === 'week') && !relativeTo) {
+    throw new RangeError(`A starting point is required for ${unit}s rounding`);
   }
 
   // First convert time units up to days, if rounding to days or higher units.
@@ -5105,8 +5099,8 @@ export function RoundDuration(
   if (unit === 'year' || unit === 'month' || unit === 'week' || unit === 'day') {
     nanoseconds = TotalDurationNanoseconds(0, hours, minutes, seconds, milliseconds, microseconds, nanoseconds, 0);
     let intermediate;
-    if (zdtRelative) {
-      intermediate = MoveRelativeZonedDateTime(zdtRelative, years, months, weeks, days);
+    if (IsTemporalZonedDateTime(relativeTo)) {
+      intermediate = MoveRelativeZonedDateTime(relativeTo, years, months, weeks, days);
     }
     let deltaDays;
     ({ days: deltaDays, nanoseconds, dayLengthNs } = NanosecondsToDays(nanoseconds, intermediate));
@@ -5117,7 +5111,8 @@ export function RoundDuration(
   let total;
   switch (unit) {
     case 'year': {
-      if (!calendar) throw new RangeError('A starting point is required for years rounding');
+      relativeTo = ToTemporalDate(relativeTo);
+      const calendar = GetSlot(relativeTo, CALENDAR);
 
       // convert months and weeks to days by calculating difference(
       // relativeTo + years, relativeTo + { years, months, weeks })
@@ -5161,7 +5156,8 @@ export function RoundDuration(
       break;
     }
     case 'month': {
-      if (!calendar) throw new RangeError('A starting point is required for months rounding');
+      relativeTo = ToTemporalDate(relativeTo);
+      const calendar = GetSlot(relativeTo, CALENDAR);
 
       // convert weeks to days by calculating difference(relativeTo +
       //   { years, months }, relativeTo + { years, months, weeks })
@@ -5196,7 +5192,9 @@ export function RoundDuration(
       break;
     }
     case 'week': {
-      if (!calendar) throw new RangeError('A starting point is required for weeks rounding');
+      relativeTo = ToTemporalDate(relativeTo);
+      const calendar = GetSlot(relativeTo, CALENDAR);
+
       // Weeks may be different lengths of days depending on the calendar,
       // convert days to weeks in a loop as described above under 'years'.
       const sign = MathSign(days);
diff --git a/spec/duration.html b/spec/duration.html
index ecc0fee81c..9930b0b2cf 100644
--- a/spec/duration.html
+++ b/spec/duration.html
@@ -1663,21 +1663,11 @@ <h1>
         1. If _relativeTo_ is not present, set _relativeTo_ to *undefined*.
         1. If _unit_ is *"year"*, *"month"*, or *"week"*, and _relativeTo_ is *undefined*, then
           1. Throw a *RangeError* exception.
-        1. Let _zonedRelativeTo_ be *undefined*.
-        1. If _relativeTo_ is not *undefined*, then
-          1. If _relativeTo_ has an [[InitializedTemporalZonedDateTime]] internal slot, then
-            1. Set _zonedRelativeTo_ to _relativeTo_.
-            1. Set _relativeTo_ to ? ToTemporalDate(_relativeTo_).
-          1. Else,
-            1. Assert: _relativeTo_ has an [[InitializedTemporalDate]] internal slot.
-          1. Let _calendar_ be _relativeTo_.[[Calendar]].
-        1. Else,
-          1. NOTE: _calendar_ will not be used below.
         1. If _unit_ is one of *"year"*, *"month"*, *"week"*, or *"day"*, then
           1. Let _nanoseconds_ be ! TotalDurationNanoseconds(0, _hours_, _minutes_, _seconds_, _milliseconds_, _microseconds_, _nanoseconds_, 0).
           1. Let _intermediate_ be *undefined*.
-          1. If _zonedRelativeTo_ is not *undefined*, then
-            1. Let _intermediate_ be ? MoveRelativeZonedDateTime(_zonedRelativeTo_, _years_, _months_, _weeks_, _days_).
+          1. If _relativeTo_ is an Object with an [[InitializedTemporalZonedDateTime]] internal slot, then
+            1. Let _intermediate_ be ? MoveRelativeZonedDateTime(_relativeTo_, _years_, _months_, _weeks_, _days_).
           1. Let _result_ be ? NanosecondsToDays(_nanoseconds_, _intermediate_).
           1. Set _days_ to _days_ + _result_.[[Days]] + _result_.[[Nanoseconds]] / _result_.[[DayLength]].
           1. Set _hours_, _minutes_, _seconds_, _milliseconds_, _microseconds_, and _nanoseconds_ to 0.
@@ -1685,6 +1675,8 @@ <h1>
           1. Let _fractionalSeconds_ be _nanoseconds_ &times; 10<sup>-9</sup> + _microseconds_ &times; 10<sup>-6</sup> + _milliseconds_ &times; 10<sup>-3</sup> + _seconds_.
         1. Let _remainder_ be *undefined*.
         1. If _unit_ is *"year"*, then
+          1. Set _relativeTo_ to ? ToTemporalDate(_relativeTo_).
+          1. Let _calendar_ be _relativeTo_.[[Calendar]].
           1. Let _yearsDuration_ be ! CreateTemporalDuration(_years_, 0, 0, 0, 0, 0, 0, 0, 0, 0).
           1. If _calendar_ is an Object, then
             1. Let _dateAdd_ be ? GetMethod(_calendar_, *"dateAdd"*).
@@ -1717,6 +1709,8 @@ <h1>
           1. Set _remainder_ to _fractionalYears_ - _years_.
           1. Set _months_, _weeks_, and _days_ to 0.
         1. Else if _unit_ is *"month"*, then
+          1. Set _relativeTo_ to ? ToTemporalDate(_relativeTo_).
+          1. Let _calendar_ be _relativeTo_.[[Calendar]].
           1. Let _yearsMonths_ be ! CreateTemporalDuration(_years_, _months_, 0, 0, 0, 0, 0, 0, 0, 0).
           1. If _calendar_ is an Object, then
             1. Let _dateAdd_ be ? GetMethod(_calendar_, *"dateAdd"*).
@@ -1744,6 +1738,8 @@ <h1>
           1. Set _remainder_ to _fractionalMonths_ - _months_.
           1. Set _weeks_ and _days_ to 0.
         1. Else if _unit_ is *"week"*, then
+          1. Set _relativeTo_ to ? ToTemporalDate(_relativeTo_).
+          1. Let _calendar_ be _relativeTo_.[[Calendar]].
           1. If _days_ &lt; 0, let _sign_ be -1; else, let _sign_ be 1.
           1. Let _oneWeek_ be ! CreateTemporalDuration(0, 0, _sign_, 0, 0, 0, 0, 0, 0, 0).
           1. If _calendar_ is an Object, then