diff --git a/src/hashset.hpp b/src/hashset.hpp
index 0137f9d9..68043ada 100644
--- a/src/hashset.hpp
+++ b/src/hashset.hpp
@@ -35,7 +35,7 @@ inline
 uint64_t
 vt_hash_const_string(const char *key_)
 {
-  int64_t hash = 0xcbf29ce484222325ull;
+  uint64_t hash = 0xcbf29ce484222325ull;
   while( *key )
     hash = ( (unsigned char)*key++ ^ hash ) * 0x100000001b3ull;