diff --git a/src/hash.c b/src/hash.c
--- a/src/hash.c
+++ b/src/hash.c
static inline khint_t
mrb_hash_ht_hash_func(mrb_state *mrb, mrb_value key)
{
- khint_t h = mrb_type(key) << 24;
+ khint_t h = (khint_t)mrb_type(key) << 24;
mrb_value h2;
h2 = mrb_funcall(mrb, key, "hash", 0, 0);