diff --git a/insns.def b/insns.def
index c6b5064794..c485f22dd0 100644
--- a/insns.def
+++ b/insns.def
@@ -519,7 +519,7 @@ newhashfromarray
 ()
 (VALUE hash)
 {
-    VM_ASSERT(num * 2 == RARRAY_LEN(ary));
+    VM_ASSERT(num * 2 == (rb_num_t)RARRAY_LEN(ary));
     hash = rb_hash_new_with_size(num);
     rb_hash_bulk_insert(num * 2, RARRAY_CONST_PTR(ary), hash);
 }