diff --git a/src/hashset.hpp b/src/hashset.hpp
index 5c8860d3..cdc730bf 100644
--- a/src/hashset.hpp
+++ b/src/hashset.hpp
@@ -78,4 +78,5 @@ public:
 
 private:
   khash_t(hashset) *_set;
+  str_set _str_set;
 };