diff --git a/ext/setup/main.php b/ext/setup/main.php
index f009e8c2..e5bfc964 100644
--- a/ext/setup/main.php
+++ b/ext/setup/main.php
@@ -134,6 +134,7 @@ class Setup extends Extension {
 			$config->set_default_string("front_page", "post/list");
 			$config->set_default_string("main_page", "post/list");
 			$config->set_default_string("base_href", "./index.php?q=");
+			$config->set_default_string("theme", "default");
 		}
 
 		if(is_a($event, 'PageRequestEvent') && ($event->page_name == "setup")) {