diff --git a/errors/env.go b/errors/env.go
index 7aaaed3..6f68030 100644
--- a/errors/env.go
+++ b/errors/env.go
@@ -12,6 +12,7 @@ var (
 	NOT_HANDLED  = errors.New("Is not handled")
 	OUT_OF_BOUND = errors.New("Out of bound")
 	NOT_SET      = errors.New("Is not set")
+	ALREADY_SET  = errors.New("Already set")
 )
 
 func WrapErr(context string, err error) error {