diff --git a/py/runtime.c b/py/runtime.c
index f7e08e37f5..65bb808a9b 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -915,6 +915,7 @@ mp_obj_t mp_iternext(mp_obj_t o_in) {
 
 // TODO: Unclear what to do with StopIterarion exception here.
 mp_vm_return_kind_t mp_resume(mp_obj_t self_in, mp_obj_t send_value, mp_obj_t throw_value, mp_obj_t *ret_val) {
+    assert((send_value != MP_OBJ_NULL) ^ (throw_value != MP_OBJ_NULL));
     mp_obj_type_t *type = mp_obj_get_type(self_in);
 
     if (type == &mp_type_gen_instance) {
diff --git a/py/vm.c b/py/vm.c
index 599a1d862e..3ffeb138c4 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -764,7 +764,7 @@ yield:
                         if (inject_exc != MP_OBJ_NULL) {
                             t_exc = inject_exc;
                             inject_exc = MP_OBJ_NULL;
-                            ret_kind = mp_resume(TOP(), mp_const_none, t_exc, &obj2);
+                            ret_kind = mp_resume(TOP(), MP_OBJ_NULL, t_exc, &obj2);
                         } else {
                             ret_kind = mp_resume(TOP(), obj1, MP_OBJ_NULL, &obj2);
                         }