diff --git a/lib/invisible_captcha/controller_ext.rb b/lib/invisible_captcha/controller_ext.rb
index b19b769..2c72e90 100644
--- a/lib/invisible_captcha/controller_ext.rb
+++ b/lib/invisible_captcha/controller_ext.rb
@@ -30,7 +30,8 @@ def on_timestamp_spam(options = {})
       if action = options[:on_timestamp_spam]
         send(action)
       else
-        redirect_back(fallback_location: root_path, flash: { error: InvisibleCaptcha.timestamp_error_message })
+        flash[:error] = InvisibleCaptcha.timestamp_error_message
+        redirect_back(fallback_location: root_path)
       end
     end