diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 1b77e800c..da8be35b0 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -385,12 +385,14 @@ class ApplicationController < ActionController::Base
   end
 
   def switch_locale(&action)
-    locale = extract_locale_from_query_params ||
+    unchecked_locale = extract_locale_from_query_params ||
       extract_locale_from_cookie ||
       extract_locale_from_user ||
       extract_locale_from_accept_language_header ||
       I18n.default_locale
 
+    locale = unchecked_locale.to_sym.in?(I18n.available_locales) ? unchecked_locale : I18n.default_locale
+
     gon.locale = locale
 
     I18n.with_locale(locale, &action)