diff --git a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
index bdbdb8a9966..d1130e1f962 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
+++ b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.cpp
@@ -50,6 +50,7 @@ void PlainYearMonthPrototype::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);
 }
 
 // 9.3.3 get Temporal.PlainYearMonth.prototype.calendarId, https://tc39.es/proposal-temporal/#sec-get-temporal.plainyearmonth.prototype.calendarid
@@ -289,4 +290,11 @@ JS_DEFINE_NATIVE_FUNCTION(PlainYearMonthPrototype::to_json)
     return PrimitiveString::create(vm, temporal_year_month_to_string(year_month, ShowCalendar::Auto));
 }
 
+// 9.3.22 Temporal.PlainYearMonth.prototype.valueOf ( ), https://tc39.es/proposal-temporal/#sec-temporal.plainyearmonth.prototype.valueof
+JS_DEFINE_NATIVE_FUNCTION(PlainYearMonthPrototype::value_of)
+{
+    // 1. Throw a TypeError exception.
+    return vm.throw_completion<TypeError>(ErrorType::Convert, "Temporal.PlainYearMonth", "a primitive value");
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h
index 2696ec31438..30a9fd1ddbe 100644
--- a/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h
+++ b/Libraries/LibJS/Runtime/Temporal/PlainYearMonthPrototype.h
@@ -42,6 +42,7 @@ 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/PlainYearMonth/PlainYearMonth.prototype.valueOf.js b/Libraries/LibJS/Tests/builtins/Temporal/PlainYearMonth/PlainYearMonth.prototype.valueOf.js
new file mode 100644
index 00000000000..6c3d2d191f4
--- /dev/null
+++ b/Libraries/LibJS/Tests/builtins/Temporal/PlainYearMonth/PlainYearMonth.prototype.valueOf.js
@@ -0,0 +1,11 @@
+describe("errors", () => {
+    test("throws TypeError", () => {
+        const plainYearMonth = new Temporal.PlainYearMonth(2021, 7);
+        expect(() => {
+            plainYearMonth.valueOf();
+        }).toThrowWithMessage(
+            TypeError,
+            "Cannot convert Temporal.PlainYearMonth to a primitive value"
+        );
+    });
+});