diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
index c3b0bbd40a..50329b0196 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.cpp
@@ -1413,7 +1413,7 @@ ThrowCompletionOr<ISODateTime> parse_temporal_zoned_date_time_string(VM& vm, Str
 }
 
 // 13.31 ParseTemporalCalendarString ( isoString ), https://tc39.es/proposal-temporal/#sec-temporal-parsetemporalcalendarstring
-ThrowCompletionOr<DeprecatedString> parse_temporal_calendar_string(VM& vm, StringView iso_string)
+ThrowCompletionOr<String> parse_temporal_calendar_string(VM& vm, StringView iso_string)
 {
     // 1. Let parseResult be Completion(ParseISODateTime(isoString)).
     auto parse_result_completion = parse_iso_date_time(vm, iso_string);
@@ -1425,10 +1425,10 @@ ThrowCompletionOr<DeprecatedString> parse_temporal_calendar_string(VM& vm, Strin
 
         // b. If calendar is undefined, return "iso8601".
         if (!calendar.has_value())
-            return "iso8601"sv;
+            return TRY_OR_THROW_OOM(vm, String::from_utf8("iso8601"sv));
         // c. Else, return calendar.
         else
-            return calendar.release_value();
+            return TRY_OR_THROW_OOM(vm, String::from_deprecated_string(*calendar));
     }
     // 3. Else,
     else {
@@ -1440,7 +1440,7 @@ ThrowCompletionOr<DeprecatedString> parse_temporal_calendar_string(VM& vm, Strin
             return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidCalendarString, iso_string);
         // c. Else, return isoString.
         else
-            return iso_string;
+            return TRY_OR_THROW_OOM(vm, String::from_utf8(iso_string));
     }
 }
 
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h b/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
index c9e5853b58..a8cfac5391 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/AbstractOperations.h
@@ -165,7 +165,7 @@ ThrowCompletionOr<ISODateTime> parse_iso_date_time(VM&, StringView iso_string);
 ThrowCompletionOr<ISODateTime> parse_iso_date_time(VM&, ParseResult const& parse_result);
 ThrowCompletionOr<TemporalInstant> parse_temporal_instant_string(VM&, StringView iso_string);
 ThrowCompletionOr<ISODateTime> parse_temporal_zoned_date_time_string(VM&, StringView iso_string);
-ThrowCompletionOr<DeprecatedString> parse_temporal_calendar_string(VM&, StringView iso_string);
+ThrowCompletionOr<String> parse_temporal_calendar_string(VM&, StringView iso_string);
 ThrowCompletionOr<TemporalDate> parse_temporal_date_string(VM&, StringView iso_string);
 ThrowCompletionOr<ISODateTime> parse_temporal_date_time_string(VM&, StringView iso_string);
 ThrowCompletionOr<DurationRecord> parse_temporal_duration_string(VM&, StringView iso_string);
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
index 41e04c6c99..9650b61423 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
@@ -34,7 +34,7 @@ Calendar::Calendar(DeprecatedString identifier, Object& prototype)
 }
 
 // 12.1.1 IsBuiltinCalendar ( id ), https://tc39.es/proposal-temporal/#sec-temporal-isbuiltincalendar
-bool is_builtin_calendar(DeprecatedString const& identifier)
+bool is_builtin_calendar(StringView identifier)
 {
     // 1. Let calendars be AvailableCalendars().
     auto calendars = available_calendars();
@@ -463,7 +463,7 @@ ThrowCompletionOr<Object*> to_temporal_calendar(VM& vm, Value temporal_calendar_
     }
 
     // 2. Let identifier be ? ToString(temporalCalendarLike).
-    auto identifier = TRY(temporal_calendar_like.to_deprecated_string(vm));
+    auto identifier = TRY(temporal_calendar_like.to_string(vm));
 
     // 3. Set identifier to ? ParseTemporalCalendarString(identifier).
     identifier = TRY(parse_temporal_calendar_string(vm, identifier));
@@ -473,7 +473,7 @@ ThrowCompletionOr<Object*> to_temporal_calendar(VM& vm, Value temporal_calendar_
         return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidCalendarIdentifier, identifier);
 
     // 5. Return ! CreateTemporalCalendar(identifier).
-    return MUST(create_temporal_calendar(vm, identifier));
+    return MUST(create_temporal_calendar(vm, identifier.to_deprecated_string()));
 }
 
 // 12.2.22 ToTemporalCalendarWithISODefault ( temporalCalendarLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporalcalendarwithisodefault
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
index 5377fb6a5e..1d1a9480c7 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
@@ -37,7 +37,7 @@ struct YearWeekRecord {
     i32 year { 0 };
 };
 
-bool is_builtin_calendar(DeprecatedString const& identifier);
+bool is_builtin_calendar(StringView identifier);
 Span<StringView const> available_calendars();
 ThrowCompletionOr<Calendar*> create_temporal_calendar(VM&, DeprecatedString const& identifier, FunctionObject const* new_target = nullptr);
 ThrowCompletionOr<Calendar*> get_builtin_calendar(VM&, DeprecatedString const& identifier);