diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 398a523..bfa4b97 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -340,7 +340,7 @@ module ApplicationHelper
           if ENV['RAILS_ENV'] == 'development' && environment.theme == 'random'
             @random_theme ||= Dir.glob('public/designs/themes/*').map { |f| File.basename(f) }.rand
             @random_theme
-          elsif ENV['RAILS_ENV'] == 'development' && params[:theme]
+          elsif ENV['RAILS_ENV'] == 'development' && params[:theme] && File.exists?(File.join(Rails.root, 'public/designs/themes', params[:theme]))
             params[:theme]
           else
             if profile && !profile.theme.nil?
--
libgit2 0.21.2