diff --git a/ruby.c b/ruby.c
index 592c584559..651bf68034 100644
--- a/ruby.c
+++ b/ruby.c
@@ -1742,7 +1742,7 @@ parse_and_compile_main(VALUE fname, const struct ruby_compile_main_arg* arg, VAL
         return NULL;
     } else {
         *error = Qnil;
-        return iseq;
+        return (ruby_opaque_t)iseq;
     }
 }