diff --git a/src/gc.c b/src/gc.c
index c082af565..270adf52f 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -1389,7 +1389,7 @@ gc_interval_ratio_set(mrb_state *mrb, mrb_value obj)
   mrb_int ratio;
 
   mrb_get_args(mrb, "i", &ratio);
-  mrb->gc.interval_ratio = ratio;
+  mrb->gc.interval_ratio = (int)ratio;
   return mrb_nil_value();
 }