diff --git a/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp b/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
index d741a3c4578..c35bdb5097f 100644
--- a/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
+++ b/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
@@ -649,21 +649,23 @@ void ECMAScriptFunctionObject::visit_edges(Visitor& visitor)
 
     visitor.visit(m_bytecode_executable);
 
-    for (auto& field : m_fields) {
-        field.initializer.visit(
-            [&visitor](GC::Ref<ECMAScriptFunctionObject>& initializer) {
-                visitor.visit(initializer);
-            },
-            [&visitor](Value initializer) {
-                visitor.visit(initializer);
-            },
-            [](Empty) {});
-        if (auto* property_key_ptr = field.name.get_pointer<PropertyKey>(); property_key_ptr && property_key_ptr->is_symbol())
-            visitor.visit(property_key_ptr->as_symbol());
-    }
+    if (m_class_data) {
+        for (auto& field : m_class_data->fields) {
+            field.initializer.visit(
+                [&visitor](GC::Ref<ECMAScriptFunctionObject>& initializer) {
+                    visitor.visit(initializer);
+                },
+                [&visitor](Value initializer) {
+                    visitor.visit(initializer);
+                },
+                [](Empty) {});
+            if (auto* property_key_ptr = field.name.get_pointer<PropertyKey>(); property_key_ptr && property_key_ptr->is_symbol())
+                visitor.visit(property_key_ptr->as_symbol());
+        }
 
-    for (auto& private_element : m_private_methods)
-        visitor.visit(private_element.value);
+        for (auto& private_element : m_class_data->private_methods)
+            visitor.visit(private_element.value);
+    }
 
     m_script_or_module.visit(
         [](Empty) {},
@@ -960,4 +962,12 @@ void ECMAScriptFunctionObject::set_name(FlyString const& name)
     m_name_string = PrimitiveString::create(vm, name);
     MUST(define_property_or_throw(vm.names.name, { .value = m_name_string, .writable = false, .enumerable = false, .configurable = true }));
 }
+
+ECMAScriptFunctionObject::ClassData& ECMAScriptFunctionObject::ensure_class_data() const
+{
+    if (!m_class_data)
+        m_class_data = make<ClassData>();
+    return *m_class_data;
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h b/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
index e9ba2439f92..95b053996b1 100644
--- a/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
+++ b/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
@@ -152,11 +152,13 @@ public:
     [[nodiscard]] ByteString const& source_text() const { return shared_data().m_source_text; }
     void set_source_text(ByteString source_text) { const_cast<SharedFunctionInstanceData&>(shared_data()).m_source_text = move(source_text); }
 
-    Vector<ClassFieldDefinition> const& fields() const { return m_fields; }
-    void add_field(ClassFieldDefinition field) { m_fields.append(move(field)); }
+    Vector<ClassFieldDefinition> const& fields() const { return ensure_class_data().fields; }
+    void add_field(ClassFieldDefinition field) { ensure_class_data().fields.append(move(field)); }
 
-    Vector<PrivateElement> const& private_methods() const { return m_private_methods; }
-    void add_private_method(PrivateElement method) { m_private_methods.append(move(method)); }
+    Vector<PrivateElement> const& private_methods() const { return ensure_class_data().private_methods; }
+    void add_private_method(PrivateElement method) { ensure_class_data().private_methods.append(move(method)); }
+
+    [[nodiscard]] bool has_class_data() const { return m_class_data; }
 
     // This is for IsSimpleParameterList (static semantics)
     bool has_simple_parameter_list() const { return shared_data().m_has_simple_parameter_list; }
@@ -211,8 +213,12 @@ private:
     GC::Ptr<Realm> m_realm;                            // [[Realm]]
     ScriptOrModule m_script_or_module;                 // [[ScriptOrModule]]
     GC::Ptr<Object> m_home_object;                     // [[HomeObject]]
-    Vector<ClassFieldDefinition> m_fields;             // [[Fields]]
-    Vector<PrivateElement> m_private_methods;          // [[PrivateMethods]]
+    struct ClassData {
+        Vector<ClassFieldDefinition> fields;    // [[Fields]]
+        Vector<PrivateElement> private_methods; // [[PrivateMethods]]
+    };
+    ClassData& ensure_class_data() const;
+    mutable OwnPtr<ClassData> m_class_data;
 };
 
 template<>
diff --git a/Libraries/LibJS/Runtime/Object.cpp b/Libraries/LibJS/Runtime/Object.cpp
index 7812d3433f6..606bd0cba90 100644
--- a/Libraries/LibJS/Runtime/Object.cpp
+++ b/Libraries/LibJS/Runtime/Object.cpp
@@ -699,6 +699,10 @@ ThrowCompletionOr<void> Object::define_field(ClassFieldDefinition const& field)
 // 7.3.34 InitializeInstanceElements ( O, constructor ), https://tc39.es/ecma262/#sec-initializeinstanceelements
 ThrowCompletionOr<void> Object::initialize_instance_elements(ECMAScriptFunctionObject& constructor)
 {
+    // AD-HOC: Avoid lazy instantiation of ECMAScriptFunctionObject::ClassData.
+    if (!constructor.has_class_data())
+        return {};
+
     // 1. Let methods be the value of constructor.[[PrivateMethods]].
     // 2. For each PrivateElement method of methods, do
     for (auto const& method : constructor.private_methods()) {