diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
index d02519dc97..2f4541e15a 100644
--- a/polyfill/lib/ecmascript.mjs
+++ b/polyfill/lib/ecmascript.mjs
@@ -1186,6 +1186,21 @@ export const ES = ObjectAssign({}, ES2020, {
     let year, month, day, hour, minute, second, millisecond, microsecond, nanosecond, calendar;
     if (ES.Type(item) === 'Object') {
       if (ES.IsTemporalDateTime(item)) return item;
+      if (ES.IsTemporalDate(item)) {
+        const TemporalPlainDateTime = GetIntrinsic('%Temporal.PlainDateTime%');
+        return new TemporalPlainDateTime(
+          GetSlot(item, ISO_YEAR),
+          GetSlot(item, ISO_MONTH),
+          GetSlot(item, ISO_DAY),
+          0,
+          0,
+          0,
+          0,
+          0,
+          0,
+          GetSlot(item, CALENDAR)
+        );
+      }
 
       calendar = item.calendar;
       if (calendar === undefined) calendar = ES.GetISO8601Calendar();
diff --git a/spec/plaindatetime.html b/spec/plaindatetime.html
index 3697202ee2..d172d41f1b 100644
--- a/spec/plaindatetime.html
+++ b/spec/plaindatetime.html
@@ -903,6 +903,8 @@ <h1>ToTemporalDateTime ( _item_ [ , _options_ ] )</h1>
         1. If Type(_item_) is Object, then
           1. If _item_ has an [[InitializedTemporalDateTime]] internal slot, then
             1. Return _item_.
+          1. If _item_ has an [[InitializedTemporalDate]] internal slot, then
+            1. Return ? CreateTemporalDateTime(_item_.[[ISOYear]], _item_.[[ISOMonth]], _item_.[[ISODay]], 0, 0, 0, 0, 0, 0, _item_.[[Calendar]]).
           1. Let _calendar_ be ? GetOptionalTemporalCalendar(_item_).
           1. Let _fieldNames_ be ? CalendarFields(_calendar_, « *"day"*, *"hour"*, *"microsecond"*, *"millisecond"*, *"minute"*, *"month"*, *"monthCode"*, *"nanosecond"*, *"second"*, *"year"* »).
           1. Let _fields_ be ? PrepareTemporalFields(_item_, _fieldNames_, «»).