diff --git a/src/challenge-module.hpp b/src/challenge-module.hpp
index 7e36d4c..af0d40b 100644
--- a/src/challenge-module.hpp
+++ b/src/challenge-module.hpp
@@ -173,6 +173,7 @@
   static const std::string WAIT_SELECTION;
   static const std::string SUCCESS;
   static const std::string PENDING;
+  static const std::string FAILURE;
 
 private:
   typedef function<unique_ptr<ChallengeModule> ()> ChallengeCreateFunc;