Thread:Project:Support desk/Cannot assign new special page ($wgSpecialPages)

I'm trying to fix Extension:ArticleComments. I need to assign "Special:ProcessComments" as new special page: $wgSpecialPages['ProcessComment'] = 'ProcessComment';

But calling the page returns Fatal error: Class 'ProcessComment' not found in /.../includes/SpecialPageFactory.php on line 337

MW 1.22, PHP 5.5.13