diff --git a/Userland/Libraries/LibJS/Runtime/Object.cpp b/Userland/Libraries/LibJS/Runtime/Object.cpp
index 1d31293670..cb5b26e6fa 100644
--- a/Userland/Libraries/LibJS/Runtime/Object.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Object.cpp
@@ -462,23 +462,49 @@ PrivateElement* Object::private_element_find(PrivateName const& name)
 // 7.3.28 PrivateFieldAdd ( O, P, value ), https://tc39.es/ecma262/#sec-privatefieldadd
 ThrowCompletionOr<void> Object::private_field_add(PrivateName const& name, Value value)
 {
+    // 1. If the host is a web browser, then
+    //    a. Perform ? HostEnsureCanAddPrivateElement(O).
+    // NOTE: Since LibJS has no way of knowing whether it is in a browser we just always call the hook.
+    TRY(vm().host_ensure_can_add_private_element(*this));
+
+    // 2. Let entry be PrivateElementFind(O, P).
+    // 3. If entry is not empty, throw a TypeError exception.
     if (auto* entry = private_element_find(name); entry)
         return vm().throw_completion<TypeError>(global_object(), ErrorType::PrivateFieldAlreadyDeclared, name.description);
+
     if (!m_private_elements)
         m_private_elements = make<Vector<PrivateElement>>();
+
+    // 4. Append PrivateElement { [[Key]]: P, [[Kind]]: field, [[Value]]: value } to O.[[PrivateElements]].
     m_private_elements->empend(name, PrivateElement::Kind::Field, value);
+
+    // 5. Return unused.
     return {};
 }
 
 // 7.3.29 PrivateMethodOrAccessorAdd ( O, method ), https://tc39.es/ecma262/#sec-privatemethodoraccessoradd
 ThrowCompletionOr<void> Object::private_method_or_accessor_add(PrivateElement element)
 {
+    // 1. Assert: method.[[Kind]] is either method or accessor.
     VERIFY(element.kind == PrivateElement::Kind::Method || element.kind == PrivateElement::Kind::Accessor);
+
+    // 2. If the host is a web browser, then
+    //    a. Perform ? HostEnsureCanAddPrivateElement(O).
+    // NOTE: Since LibJS has no way of knowing whether it is in a browser we just always call the hook.
+    TRY(vm().host_ensure_can_add_private_element(*this));
+
+    // 3. Let entry be PrivateElementFind(O, method.[[Key]]).
+    // 4. If entry is not empty, throw a TypeError exception.
     if (auto* entry = private_element_find(element.key); entry)
         return vm().throw_completion<TypeError>(global_object(), ErrorType::PrivateFieldAlreadyDeclared, element.key.description);
+
     if (!m_private_elements)
         m_private_elements = make<Vector<PrivateElement>>();
+
+    // 5. Append method to O.[[PrivateElements]].
     m_private_elements->append(move(element));
+
+    // 6. Return unused.
     return {};
 }
 
diff --git a/Userland/Libraries/LibJS/Runtime/VM.cpp b/Userland/Libraries/LibJS/Runtime/VM.cpp
index a7a12df189..5156515ade 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.cpp
+++ b/Userland/Libraries/LibJS/Runtime/VM.cpp
@@ -124,6 +124,21 @@ VM::VM(OwnPtr<CustomData> custom_data)
         return {};
     };
 
+    host_ensure_can_add_private_element = [](Object&) -> ThrowCompletionOr<void> {
+        // The host-defined abstract operation HostEnsureCanAddPrivateElement takes argument O (an Object)
+        // and returns either a normal completion containing unused or a throw completion.
+        // It allows host environments to prevent the addition of private elements to particular host-defined exotic objects.
+        // An implementation of HostEnsureCanAddPrivateElement must conform to the following requirements:
+        // - If O is not a host-defined exotic object, this abstract operation must return NormalCompletion(unused) and perform no other steps.
+        // - Any two calls of this abstract operation with the same argument must return the same kind of Completion Record.
+        // The default implementation of HostEnsureCanAddPrivateElement is to return NormalCompletion(unused).
+        return {};
+
+        // This abstract operation is only invoked by ECMAScript hosts that are web browsers.
+        // NOTE: Since LibJS has no way of knowing whether the current environment is a browser we always
+        //       call HostEnsureCanAddPrivateElement when needed.
+    };
+
 #define __JS_ENUMERATE(SymbolName, snake_name) \
     m_well_known_symbol_##snake_name = js_symbol(*this, "Symbol." #SymbolName, false);
     JS_ENUMERATE_WELL_KNOWN_SYMBOLS
diff --git a/Userland/Libraries/LibJS/Runtime/VM.h b/Userland/Libraries/LibJS/Runtime/VM.h
index 4f7dc2b8db..9a5b4c71c3 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.h
+++ b/Userland/Libraries/LibJS/Runtime/VM.h
@@ -229,6 +229,7 @@ public:
     Function<void(Function<ThrowCompletionOr<Value>()>, Realm*)> host_enqueue_promise_job;
     Function<JobCallback(FunctionObject&)> host_make_job_callback;
     Function<ThrowCompletionOr<void>(Realm&)> host_ensure_can_compile_strings;
+    Function<ThrowCompletionOr<void>(Object&)> host_ensure_can_add_private_element;
 
 private:
     explicit VM(OwnPtr<CustomData>);