2 files changed, 10 insertions, 5 deletions
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
index 24d709556b..fcbd858ebc 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
@@ -575,10 +575,11 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_string)
 JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_json)
 {
     // 1. Let calendar be the this value.
-    auto calendar = vm.this_value(global_object);
+    // 2. Perform ? RequireInternalSlot(calendar, [[InitializedTemporalCalendar]]).
+    auto* calendar = TRY(typed_this_object(global_object));
 
-    // 2. Return ? ToString(calendar).
-    return js_string(vm, TRY(calendar.to_string(global_object)));
+    // 3. Return ? ToString(calendar).
+    return js_string(vm, TRY(Value(calendar).to_string(global_object)));
 }
 
 // 15.6.2.6 Temporal.Calendar.prototype.era ( temporalDateLike ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.era
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toJSON.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toJSON.js
index 703283b897..6470c47bcf 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toJSON.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.toJSON.js
@@ -7,8 +7,12 @@ describe("correct behavior", () => {
         const calendar = new Temporal.Calendar("iso8601");
         expect(calendar.toJSON()).toBe("iso8601");
     });
+});
 
-    test("works with any this value", () => {
-        expect(Temporal.Calendar.prototype.toJSON.call("foo")).toBe("foo");
+describe("errors", () => {
+    test("this value must be a Temporal.Calendar object", () => {
+        expect(() => {
+            Temporal.Calendar.prototype.toJSON.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.Calendar");
     });
 });