diff --git a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
index dfd40381a7f..c7b5c3f854b 100644
--- a/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DatePrototype.cpp
@@ -731,17 +731,29 @@ JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_string)
     return js_string(vm, move(formatted));
 }
 
-// 21.4.4.40 Date.prototype.toLocaleTimeString ( [ reserved1 [ , reserved2 ] ] ), https://tc39.es/ecma262/#sec-date.prototype.tolocaletimestring
+// 18.4.3 Date.prototype.toLocaleTimeString ( [ locales [ , options ] ] ), https://tc39.es/ecma402/#sup-date.prototype.tolocaletimestring
 JS_DEFINE_NATIVE_FUNCTION(DatePrototype::to_locale_time_string)
 {
+    auto locales = vm.argument(0);
+    auto options = vm.argument(1);
+
+    // 1. Let x be ? thisTimeValue(this value).
     auto* this_object = TRY(typed_this_object(global_object));
+    auto time = this_object->is_invalid() ? js_nan() : this_object->value_of();
 
-    if (this_object->is_invalid())
-        return js_string(vm, "Invalid Date");
+    // 2. If x is NaN, return "Invalid Date".
+    if (time.is_nan())
+        return js_string(vm, "Invalid Date"sv);
 
-    // FIXME: Optional locales, options params.
-    auto string = this_object->locale_time_string();
-    return js_string(vm, move(string));
+    // 3. Let options be ? ToDateTimeOptions(options, "time", "time").
+    options = Value(TRY(Intl::to_date_time_options(global_object, options, Intl::OptionRequired::Time, Intl::OptionDefaults::Time)));
+
+    // 4. Let timeFormat be ? Construct(%DateTimeFormat%, « locales, options »).
+    auto* time_format = TRY(construct_date_time_format(global_object, locales, options));
+
+    // 5. Return ? FormatDateTime(dateFormat, x).
+    auto formatted = TRY(Intl::format_date_time(global_object, *time_format, time));
+    return js_string(vm, move(formatted));
 }
 
 // 21.4.4.42 Date.prototype.toTimeString ( ), https://tc39.es/ecma262/#sec-date.prototype.totimestring
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js
new file mode 100644
index 00000000000..6d85632f8ea
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Date/Date.prototype.toLocaleTimeString.js
@@ -0,0 +1,63 @@
+describe("errors", () => {
+    test("called on non-Date object", () => {
+        expect(() => {
+            Date.prototype.toLocaleTimeString();
+        }).toThrowWithMessage(TypeError, "Not an object of type Date");
+    });
+
+    test("called with value that cannot be converted to a number", () => {
+        expect(() => {
+            new Date(Symbol.hasInstance).toLocaleTimeString();
+        }).toThrowWithMessage(TypeError, "Cannot convert symbol to number");
+
+        expect(() => {
+            new Date(1n).toLocaleTimeString();
+        }).toThrowWithMessage(TypeError, "Cannot convert BigInt to number");
+    });
+
+    test("time value cannot be clipped", () => {
+        expect(() => {
+            new Date(-8.65e15).toLocaleTimeString();
+        }).toThrowWithMessage(RangeError, "Time value must be between -8.64E15 and 8.64E15");
+    });
+
+    test("dateStyle may not be specified", () => {
+        expect(() => {
+            new Date().toLocaleTimeString([], { dateStyle: "short" });
+        }).toThrowWithMessage(TypeError, "Option dateStyle cannot be set when also providing time");
+    });
+});
+
+describe("correct behavior", () => {
+    test("NaN", () => {
+        const d = new Date(NaN);
+        expect(d.toLocaleTimeString()).toBe("Invalid Date");
+    });
+
+    const d0 = new Date(Date.UTC(2021, 11, 7, 17, 40, 50, 456));
+    const d1 = new Date(Date.UTC(1989, 0, 23, 7, 8, 9, 45));
+
+    test("defaults to time", () => {
+        expect(d0.toLocaleTimeString("en", { timeZone: "UTC" })).toBe("5:40:50 PM");
+        expect(d1.toLocaleTimeString("en", { timeZone: "UTC" })).toBe("7:08:09 AM");
+
+        expect(d0.toLocaleTimeString("ar", { timeZone: "UTC" })).toBe("٥:٤٠:٥٠ م");
+        expect(d1.toLocaleTimeString("ar", { timeZone: "UTC" })).toBe("٧:٠٨:٠٩ ص");
+    });
+
+    test("timeStyle may be set", () => {
+        expect(d0.toLocaleTimeString("en", { timeStyle: "long", timeZone: "UTC" })).toBe(
+            "5:40:50 PM UTC"
+        );
+        expect(d1.toLocaleTimeString("en", { timeStyle: "long", timeZone: "UTC" })).toBe(
+            "7:08:09 AM UTC"
+        );
+
+        expect(d0.toLocaleTimeString("ar", { timeStyle: "long", timeZone: "UTC" })).toBe(
+            "٥:٤٠:٥٠ م UTC"
+        );
+        expect(d1.toLocaleTimeString("ar", { timeStyle: "long", timeZone: "UTC" })).toBe(
+            "٧:٠٨:٠٩ ص UTC"
+        );
+    });
+});