diff --git a/src/vm.c b/src/vm.c
index 91ab6793f..238d32dae 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1741,7 +1741,7 @@ RETRY_TRY_BLOCK:
       if (argc < 0) {
         struct RArray *ary = mrb_ary_ptr(regs[1]);
         argv = ARY_PTR(ary);
-        argc = ARY_LEN(ary);
+        argc = (int)ARY_LEN(ary);
         mrb_gc_protect(mrb, regs[1]);
       }
       if (mrb->c->ci->proc && MRB_PROC_STRICT_P(mrb->c->ci->proc)) {