diff --git a/middleman-core/lib/middleman-core/preview_server.rb b/middleman-core/lib/middleman-core/preview_server.rb
index 2edeb849..ff3e0c14 100644
--- a/middleman-core/lib/middleman-core/preview_server.rb
+++ b/middleman-core/lib/middleman-core/preview_server.rb
@@ -145,7 +145,6 @@ module Middleman
       # @param [Middleman::Application] app
       # @return [void]
       def mount_instance
-        @app = new_app
         @webrick ||= setup_webrick(
           @options[:host]  || "0.0.0.0",
           @options[:debug] || false