diff --git a/src/hashset.hpp b/src/hashset.hpp
index ce962a1f..b6d6934b 100644
--- a/src/hashset.hpp
+++ b/src/hashset.hpp
@@ -104,10 +104,10 @@ public:
   }
 
   inline
-  int
+  size_t
   size(void)
   {
-    return u64_set_size(&_str_set);
+    return u64_set_size(&_u64_set);
     return kh_size(_set);
   }