diff --git a/py/objnone.c b/py/objnone.c
index c79c818..fc55132 100644
--- a/py/objnone.c
+++ b/py/objnone.c
@@ -18,7 +18,7 @@
 STATIC mp_obj_t none_unary_op(int op, mp_obj_t o_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return mp_const_false;
-        default: return MP_OBJ_NULL; // op not supported for None
+        default: return MP_OBJ_NOT_SUPPORTED;
     }
 }