diff --git a/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp
index 8466178f6cb..f51d6f9addd 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.cpp
@@ -46,6 +46,7 @@ void PlainTimePrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.toString, to_string, 0, attr);
     define_native_function(realm, vm.names.toLocaleString, to_locale_string, 0, attr);
     define_native_function(realm, vm.names.toJSON, to_json, 0, attr);
+    define_native_function(realm, vm.names.valueOf, value_of, 0, attr);
 }
 
 // 4.3.3 get Temporal.PlainTime.prototype.hour, https://tc39.es/proposal-temporal/#sec-get-temporal.plaintime.prototype.hour
@@ -336,4 +337,11 @@ JS_DEFINE_NATIVE_FUNCTION(PlainTimePrototype::to_json)
     return PrimitiveString::create(vm, time_record_to_string(temporal_time->time(), Auto {}));
 }
 
+// 4.3.19 Temporal.PlainTime.prototype.valueOf ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaintime.prototype.valueof
+JS_DEFINE_NATIVE_FUNCTION(PlainTimePrototype::value_of)
+{
+    // 1. Throw a TypeError exception.
+    return vm.throw_completion<TypeError>(ErrorType::Convert, "Temporal.PlainTime", "a primitive value");
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.h b/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.h
index ef940aa6749..7e680726507 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainTimePrototype.h
@@ -39,6 +39,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_locale_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
+    JS_DECLARE_NATIVE_FUNCTION(value_of);
 };
 
 }
diff --git a/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.prototype.valueOf.js b/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.prototype.valueOf.js
new file mode 100644
index 00000000000..71a1988d106
--- /dev/null
+++ b/Libraries/LibJS/Tests/builtins/Temporal/PlainTime/PlainTime.prototype.valueOf.js
@@ -0,0 +1,7 @@
+describe("errors", () => {
+    test("throws TypeError", () => {
+        expect(() => {
+            new Temporal.PlainTime(19, 54, 38).valueOf();
+        }).toThrowWithMessage(TypeError, "Cannot convert Temporal.PlainTime to a primitive value");
+    });
+});