public function propertyChanged($sender, $propertyName, $oldValue, $newValue)
    {
        if (!$sender instanceof MutableAclInterface && !$sender instanceof EntryInterface) {
            throw new \InvalidArgumentException('$sender must be an instance of MutableAclInterface, or EntryInterface.');
        }

        if ($sender instanceof EntryInterface) {
            if (null === $sender->getId()) {
                return;
            }

            $ace = $sender;
            $sender = $ace->getAcl();
        } else {
            $ace = null;
        }

        if (false === $this->propertyChanges->contains($sender)) {
            throw new \InvalidArgumentException('$sender is not being tracked by this provider.');
        }

        $propertyChanges = $this->propertyChanges->offsetGet($sender);
        if (null === $ace) {
            if (isset($propertyChanges[$propertyName])) {
                $oldValue = $propertyChanges[$propertyName][0];
                if ($oldValue === $newValue) {
                    unset($propertyChanges[$propertyName]);
                } else {
                    $propertyChanges[$propertyName] = array($oldValue, $newValue);
                }
            } else {
                $propertyChanges[$propertyName] = array($oldValue, $newValue);
            }
        } else {
            if (!isset($propertyChanges['aces'])) {
                $propertyChanges['aces'] = new \SplObjectStorage();
            }

            $acePropertyChanges = $propertyChanges['aces']->contains($ace) ? $propertyChanges['aces']->offsetGet($ace) : array();

            if (isset($acePropertyChanges[$propertyName])) {
                $oldValue = $acePropertyChanges[$propertyName][0];
                if ($oldValue === $newValue) {
                    unset($acePropertyChanges[$propertyName]);
                } else {
                    $acePropertyChanges[$propertyName] = array($oldValue, $newValue);
                }
            } else {
                $acePropertyChanges[$propertyName] = array($oldValue, $newValue);
            }

            if (count($acePropertyChanges) > 0) {
                $propertyChanges['aces']->offsetSet($ace, $acePropertyChanges);
            } else {
                $propertyChanges['aces']->offsetUnset($ace);

                if (0 === count($propertyChanges['aces'])) {
                    unset($propertyChanges['aces']);
                }
            }
        }

        $this->propertyChanges->offsetSet($sender, $propertyChanges);
    }