diff --git a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
index 56696a9b2b..8d74984245 100644
--- a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
@@ -72,10 +72,10 @@ void DatePrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.setMonth, set_month, 2, attr);
     define_native_function(vm.names.setSeconds, set_seconds, 2, attr);
     define_native_function(vm.names.setTime, set_time, 1, attr);
-    define_native_function(vm.names.setUTCDate, set_date, 1, attr);                 // FIXME: This is a hack, Serenity doesn't currently support timezones other than UTC.
-    define_native_function(vm.names.setUTCFullYear, set_full_year, 3, attr);        // FIXME: see above
-    define_native_function(vm.names.setUTCHours, set_hours, 4, attr);               // FIXME: see above
-    define_native_function(vm.names.setUTCMilliseconds, set_milliseconds, 1, attr); // FIXME: see above
+    define_native_function(vm.names.setUTCDate, set_date, 1, attr);          // FIXME: This is a hack, Serenity doesn't currently support timezones other than UTC.
+    define_native_function(vm.names.setUTCFullYear, set_full_year, 3, attr); // FIXME: see above
+    define_native_function(vm.names.setUTCHours, set_hours, 4, attr);        // FIXME: see above
+    define_native_function(vm.names.setUTCMilliseconds, set_utc_milliseconds, 1, attr);
     define_native_function(vm.names.setUTCMinutes, set_utc_minutes, 3, attr);
     define_native_function(vm.names.setUTCMonth, set_utc_month, 2, attr);
     define_native_function(vm.names.setUTCSeconds, set_utc_seconds, 2, attr);
@@ -619,6 +619,35 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_time)
     return time;
 }
 
+// 21.4.4.31 Date.prototype.setUTCMilliseconds ( ms ), https://tc39.es/ecma262/#sec-date.prototype.setutcmilliseconds
+JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_utc_milliseconds)
+{
+    // 1. Let t be ? thisTimeValue(this value).
+    auto this_time = TRY(this_time_value(global_object, vm.this_value(global_object)));
+    auto time = local_time(this_time.as_double());
+
+    // 2. Let milli be ? ToNumber(ms).
+    auto millisecond = TRY(vm.argument(0).to_number(global_object));
+
+    // 3. Let time be MakeTime(HourFromTime(t), MinFromTime(t), SecFromTime(t), milli).
+    auto hour = Value(hour_from_time(time));
+    auto minute = Value(min_from_time(time));
+    auto second = Value(sec_from_time(time));
+
+    auto new_time = make_time(global_object, hour, minute, second, millisecond);
+
+    // 4. Let v be TimeClip(MakeDate(Day(t), time)).
+    auto date = make_date(Value(day(time)), new_time);
+    date = time_clip(global_object, date);
+
+    // 5. Set the [[DateValue]] internal slot of this Date object to v.
+    auto* this_object = MUST(typed_this_object(global_object));
+    this_object->set_date_value(date.as_double());
+
+    // 6. Return v.
+    return date;
+}
+
 // 21.4.4.32 Date.prototype.setUTCMinutes ( min [ , sec [ , ms ] ] ), https://tc39.es/ecma262/#sec-date.prototype.setutcminutes
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::set_utc_minutes)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/DatePrototype.h b/Userland/Libraries/LibJS/Runtime/DatePrototype.h
index c0c49b0dfb..619c8dbd2d 100644
--- a/Userland/Libraries/LibJS/Runtime/DatePrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/DatePrototype.h
@@ -46,6 +46,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(set_month);
     JS_DECLARE_NATIVE_FUNCTION(set_seconds);
     JS_DECLARE_NATIVE_FUNCTION(set_time);
+    JS_DECLARE_NATIVE_FUNCTION(set_utc_milliseconds);
     JS_DECLARE_NATIVE_FUNCTION(set_utc_minutes);
     JS_DECLARE_NATIVE_FUNCTION(set_utc_month);
     JS_DECLARE_NATIVE_FUNCTION(set_utc_seconds);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setUTCMilliseconds.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setUTCMilliseconds.js
new file mode 100644
index 0000000000..236006e70b
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.setUTCMilliseconds.js
@@ -0,0 +1,38 @@
+describe("errors", () => {
+    test("called on non-Date object", () => {
+        expect(() => {
+            Date.prototype.setUTCMilliseconds();
+        }).toThrowWithMessage(TypeError, "Not an object of type Date");
+    });
+
+    test("called with non-numeric parameters", () => {
+        expect(() => {
+            new Date().setUTCMilliseconds(Symbol.hasInstance);
+        }).toThrowWithMessage(TypeError, "Cannot convert symbol to number");
+    });
+});
+
+describe("correct behavior", () => {
+    const d = new Date(2000, 2, 1);
+
+    test("basic functionality", () => {
+        d.setUTCMilliseconds(8);
+        expect(d.getUTCMilliseconds()).toBe(8);
+
+        d.setUTCMilliseconds("");
+        expect(d.getUTCMilliseconds()).toBe(0);
+
+        d.setUTCMilliseconds("a");
+        expect(d.getUTCMilliseconds()).toBe(NaN);
+    });
+
+    test("NaN", () => {
+        d.setUTCMilliseconds(NaN);
+        expect(d.getUTCMilliseconds()).toBeNaN();
+    });
+
+    test("time clip", () => {
+        d.setUTCMilliseconds(8.65e15);
+        expect(d.getUTCMilliseconds()).toBeNaN();
+    });
+});