diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp
index e4ba059cd5..8673ab2de4 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.cpp
@@ -15,7 +15,7 @@
 namespace JS::Temporal {
 
 // 5 Temporal.PlainDateTime Objects, https://tc39.es/proposal-temporal/#sec-temporal-plaindatetime-objects
-PlainDateTime::PlainDateTime(i32 iso_year, u8 iso_month, u8 iso_day, u8 iso_hour, u8 iso_minute, u8 iso_second, u8 iso_millisecond, u8 iso_microsecond, u8 iso_nanosecond, Object& calendar, Object& prototype)
+PlainDateTime::PlainDateTime(i32 iso_year, u8 iso_month, u8 iso_day, u8 iso_hour, u8 iso_minute, u8 iso_second, u16 iso_millisecond, u16 iso_microsecond, u16 iso_nanosecond, Object& calendar, Object& prototype)
     : Object(prototype)
     , m_iso_year(iso_year)
     , m_iso_month(iso_month)
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h
index 9e062565d0..9836d0ea7b 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTime.h
@@ -16,7 +16,7 @@ class PlainDateTime final : public Object {
     JS_OBJECT(PlainDateTime, Object);
 
 public:
-    PlainDateTime(i32 iso_year, u8 iso_month, u8 iso_day, u8 iso_hour, u8 iso_minute, u8 iso_second, u8 iso_millisecond, u8 iso_microsecond, u8 iso_nanosecond, Object& calendar, Object& prototype);
+    PlainDateTime(i32 iso_year, u8 iso_month, u8 iso_day, u8 iso_hour, u8 iso_minute, u8 iso_second, u16 iso_millisecond, u16 iso_microsecond, u16 iso_nanosecond, Object& calendar, Object& prototype);
     virtual ~PlainDateTime() override = default;
 
     [[nodiscard]] i32 iso_year() const { return m_iso_year; }
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.getISOFields.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.getISOFields.js
index ecfe2b1487..1204a08eb6 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.getISOFields.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.getISOFields.js
@@ -22,11 +22,11 @@ describe("normal behavior", () => {
             calendar: calendar,
             isoDay: 23,
             isoHour: 0,
-            isoMicrosecond: 200,
+            isoMicrosecond: 456,
             isoMillisecond: 123,
             isoMinute: 42,
             isoMonth: 7,
-            isoNanosecond: 21,
+            isoNanosecond: 789,
             isoSecond: 18,
             isoYear: 2021,
         });